Alexander Zverev was given a thorough examination of his Paris Masters credentials by Grigor Dimitrov, but the fourth seed progressed nonetheless to reach the last eight.

Zverev, who last in last year's final, saw match points slip from his grasp in the second set as Dimitrov levelled the match, however, he eventually prevailed on Thursday.

World number one Novak Djokovic benefited from a walkover, while Daniil Medvedev also moved through to the quarter-finals of the ATP Masters 1000 event.

Zverev outlasts Dimitrov

Olympic Games gold medallist Zverev had to dig deep for his 7-6 (7-4) 6-7 (3-7) 6-3 win over former world number three Dimitrov.

It was Zverev's seventh win on the bounce, but he was well aware of just how deep he had to dig to see off a resilient Dimitrov.

"Incredible match," Zverev, who won a fifth tour title of the year last week at the Vienna Open, said afterwards. "Grigor is playing very high-level tennis and I had to leave everything out there.

"I think it was a very high-level match and it could have gone both ways, especially the third set. I am happy with how things went in the end."

Djokovic moves through without playing

There was no such ordeal for top seed Djokovic, however.

Djokovic – a 20-time grand slam champion – received a walkover after Gael Monfils was advised not to continue with the tournament due to an adductor issue sustained in his previous win over Adrian Mannarino.

Taylor Fritz awaits five-time Paris champion Djokovic after the American saw off 10th seed Norrie 6-3 7-6 (7-3), while Casper Ruud will tussle with Zverev.

Ruud's emphatic 6-2 6-1 demolition of Marcos Giron clinched a historic achievement for the 22-year-old – who became the first Norwegian to qualify for the ATP Finals at the end of a breakthrough year in which no player can better his five tour-level titles.

Hubert Hurkacz did his chances of joining Ruud in Turin no harm as the Polish seventh seed – who holds the last automatic qualifying berth – fought back to defeat Dominik Koepfer 4-6 7-5 6-2 and set up a meeting with James Duckworth, who beat Alexei Popyrin 7-6 (8-6) 6-4.

Second seed and US Open champion Medvedev was another who had to come from behind before ultimately seeing off Sebastian Korda 4-6 6-1 6-3.

He will go up against Hugo Gaston, who became the first French qualifier to reach the Paris Masters quarter-finals since 1990 with his win over Carlos Alcaraz.

Gael Monfils has withdrawn from the Paris Masters due to an adductor problem, handing world number one Novak Djokovic a walkover into the quarter-finals.

Djokovic has played only once on the ATP Tour since losing the US Open final to Daniil Medvedev on September 12.

That defeat at Flushing Meadows ended Djokovic's hopes of achieving a calendar Grand Slam, though the Serbian has returned to action for the final few weeks of the 2021 season.

With the ATP Finals coming up, Djokovic headed to Paris looking to regain the title he claimed in his last appearance in the tournament back in 2019. He needed three sets, but overcame Marton Fucsovics 6-2 4-6 6-3 in his first match.

He has won the Paris Masters on five occasions and is the top seed this time around, with defending champion Medvedev seeded second. 

Monfils, seeded 15th, beat Miomir Kecmanovic and Adrian Mannarino en route to the last 16, but confirmed to the media on Thursday that he had been advised not to continue.

Djokovic will face the winner of Cameron Norrie, who recently triumphed at Indian Wells, and Taylor Fritz in the quarter-finals.

The field has already been cleared of third seed Stefanos Tsitsipas, who retired hurt when facing Alexei Popyrin on Wednesday.

Teenage sensation Carlos Alcaraz put in an impressive display to upstage eighth seed Jannik Sinner in straights sets in the third round of the ATP Paris Masters on Wednesday.

Alcaraz was on top for most of his 7-6 (7-1) 7-5 victory, winning 80 per cent of his first-serve points and 75 per cent of net points against Sinner.

Sinner showed determination to stay in both sets, with the Italian saving nine of the 11 break points he faced, but it was ultimately in vain.

The European Open winner will be among those sweating as the race to qualify for the ATP Finals in Turin heats up.

After the win, 18-year-old Alcaraz said: "I'm so happy for this win as Jannik was fighting for a spot at the ATP Finals. It's my third Top 10 win of the year.

"I think Jannik and I will have a great rivalry in the future... I think that I played really, really aggressive, more than him. I think that was one of the keys."

Alcaraz will now face qualifier Hugo Gaston in the next round after the Frenchman impressively knocked out 12th seed Pablo Carreno Busta 6-7 (3-7) 6-4 7-5.

Interesting day for Turin hopefuls

It was a mixed day for others looking to secure a spot at the season-ending ATP Finals later this month as Felix Auger-Aliassime – ranked 12th in the ATP Race to Turin – lost in straight sets to Dominik Koepfer, who added to his impressive list of victims after beating three-time grand slam champion Andy Murray in the first round.

Koepfer will play another Turin hopeful, the 10th-ranked Hubert Hurkacz after he beat Tommy Paul in straight sets.

Cameron Norrie also impressed in his 6-3 6-4 win over Reilly Opelka, which was his 50th tour-level win of the year.

Taylor Fritz awaits after the American stunned fifth seed Andrey Rublev 7-5 7-6 (7-2).

Medvedev and Zverev ease through but Tsitsipas out

Second seed and US Open champion Daniil Medvedev had a routine first match of the tournament as he swept past Ilya Ivashka 7-5 6-4, while Olympic Games gold medallist and fourth seed Alexander Zverev also had few problems against Dusan Lajovic 6-3 7-6 (7-5).

However, third seed Stefanos Tsitsipas exited after retiring hurt with an apparent arm injury against Alexei Popyrin in the first set with the score at 4-2 to the Australian.

Popyrin will now face fellow countryman James Duckworth, who followed up his impressive win against 14th seed Roberto Bautista Agut with a 6-3 3-6 6-3 victory against Lorenzo Musetti.

Elsewhere, 11th seed Diego Schwartzman was shocked by qualifier Marcos Giron 7-6 (7-2) 7-6 (7-4).

There were also wins for 16th seed Grigor Dimitrov against Karen Kachanov, and Sebastian Korda over Marin Cilic.

Gael Monfils will go up against world number one Novak Djokovic in the third round after the experienced French 15th seed came from behind to beat compatriot Adrian Mannarino 2-6 7-6 (7-4) 6-2.

Novak Djokovic recovered from a second-set blip to emerge victorious 6-2 4-6 6-3 in his first match since the US Open at the Paris Masters.

Victory in Paris would see Djokovic – competing for the first time since September's loss to Daniil Medvedev in the Flushing Meadows final – clinch the year-end number one ranking for a record seventh time.

Djokovic looked to be on course for a routine victory to start his campaign after comfortably taking the first set against Marton Fucsovics in their second-round contest on Tuesday.

However, the top seed's Hungarian opponent fought back to force a decider, hitting 13 winners to seven unforced errors in the second set.

But Djokovic – a record five-time Paris Masters champion – ensured a remarkable turnaround was not forthcoming, breaking Fucsovics twice in the third and, after letting one match point slip, clinching his second to secure victory.

Felix fights back

Ranked 12th in the ATP Race to Turin, Felix Auger-Aliassime needs to lift the trophy in Paris and hope Casper Ruud and Jannik Sinner do not reach the latter stages to make it to the ATP Finals.

Auger-Aliassime risked falling at the first hurdle on Tuesday as the ninth seed was forced to fight back to defeat Gianluca Mager 4-6 6-4 6-1.

"I had difficulty with my pace at the beginning of the match," said Auger-Aliassime. "I didn't hit enough first serves so I had a bit of pressure on my second serve.

"So I could have served better in the first set. I [had] a poor game at four-all and I got broken, but even before that there were moments at 30-all it was a bit hot and a bit tight. I think I relaxed. I found a better pace at the beginning of the second set, and it went even better as the match went forward."

He will next face Dominik Koepfer in the second round following the German's stunning win over Andy Murray on Monday.

Alcaraz sets up Sinner clash

Sinner will have an extremely testing second-round clash after Carlos Alcaraz came from behind to see off wild card Pierre Hugues-Herbert.

Alcaraz let slip a 4-2 lead in the first set to lose that on a tie-break but won six straight points in a second-set breaker before eventually battling to a 6-7 (4-7) 7-6 (7-2) 7-5 win in two hours, 53 minutes.

"It's not easy to play against a home player," Alcaraz said. "I think we played a good level and it was a great match, so I am happy to win. He has a great serve, so I had to return better and remain focus. I think that was the key. I am playing at a good level and I want to finish the year strong."

Diego Schwartzman – the 11th seed – needed three sets to see off John Millman, 15th seed Gael Monfils reversed a one-set deficit against Miomir Kecmanovic and 16th seed Grigor Dimitrov survived a three-setter with Richard Gasquet.

But one seed did fall on Tuesday, Roberto Bautista Agut (14) edged by James Duckworth in three sets.

Dominic Thiem has confirmed he has been given a coronavirus vaccine and will return to action in Abu Dhabi next month with the objective of playing in the 2022 Australian Open.

The 2020 US Open champion has been out of action since suffering a wrist injury at the Mallorca Championships in June.

Thiem on Tuesday revealed he has made good progress with his recovery and will play in the World Tennis Championship, an exhibition event that will be staged from December 16-18.

The 28-year-old had stated he wanted to wait for a Novavax jab, but was urged by Austrian minister for Social Affairs, Health, Care and Consumer Protection Wolfgang Muckstein to take an alternative vaccine as his preferred choice would not be available until next year.

Thiem says he has now been vaccinated and is relishing getting back on court as he eyes a grand slam return in Melbourne in January.

"I am very happy to announce that my recovery is going well. The MRI I did today showed that my wrist injury has improved significantly," Thiem tweeted on Tuesday.

"A couple of weeks ago I started playing with soft balls and was able to switch to normal tennis balls during yesterday's practice session. My team and I strongly believe that I'll be ready to make my comeback later this year.

"I'll be returning to competition in December and will be playing the MWTC 2021 in Abu Dhabi – with the objective to return to the Tour for the 2022 Australian Open.

"Needless to say that the vaccine is needed to play both events, and in my case I have already been vaccinated. I saw recently some news about this and I had to make it very clear that I would get vaccinated. Hopefully the next time things won't be taken this far [sic] as I saw last week..."

Rafael Nadal is also set to return from injury in Abu Dhabi.

Andy Murray was defeated in the first round of the Paris Masters on Monday following a three-set battle with Dominik Koepfer.

Murray, given a wildcard entry, was initially drawn against Jenson Brooksby but the American withdrew just a couple of hours before the match was due to start because of an abdominal injury.

The three-time major singles champion instead faced German Koepfer, who triumphed 6-4 5-7 7-6 (11-9) in a contest lasting just over three hours.

Lucky loser Koepfer, in his debut in the main draw, served for the match at 5-3 in the second set but was broken to love as the contest turned topsy-turvy.

Murray had seven match points in the decider, including five in the tie-breaker, but the 2016 champion could not convert and left the court looking disconsolate.

"I was about to go back to the hotel and then one of the ATP Tour Managers texted me, 'Dom, you in? You're playing against Andy Murray'," Koepfer said. "Honestly, I was a little nervous.

"I didn't expect to play today, I was hoping that someone was going to pull out tomorrow. But a night match here in Paris, a lot of fans, they had an unbelievable crowd, the first time for me for a while. It's been a great day. Unexpected, but it worked out and I'm happy."

There was more disappointment for the United Kingdom as Dan Evans saw a strong start yield nothing as he lost in three sets to Alexander Bublik, who goes on to face sixth seed Casper Ruud.

Djokovic set for Fucsovics test

World number one Novak Djokovic will begin his campaign against Marton Fucsovics, who outlasted Fabio Fognini in a match lasing nearly two hours and 45 minutes.

Fucsovics dominated the first set but was engaged in a far tougher battle for the rest of the contest before winning 6-1 6-7 (6-8) 7-6 (7-5).

The Hungarian is 0-3 against Djokovic in his career, last losing to the 20-time major winner at the quarter-final stage of Wimbledon. The winner of this latest contest could face a last-16 meeting with Adrian Mannarino, who won in straight sets against Nikoloz Basilashvili.

Ilya Ivashka overcame Albert Ramos-Vinolas to secure a meeting with second seed Daniil Medvedev, while Dusan Lajovic will face Alexander Zverev after defeating Mackenzie McDonald.

Norrie brings up Tour century to keep Finals in sight

Tenth seed Cameron Norrie kept his chances alive of qualifying for the ATP Finals after a commanding 6-2 6-1 defeat of Federico Delbonis.

The Briton's victory, his 100th on the Tour, could help him to close the gap in the race for the year-ending tournament in Turin. Norrie started the week in 11th place, 140 points adrift of Jannik Sinner in the eighth and final automatic qualifying spot.

"It's obviously a great milestone and it shows I have been on the Tour and have a little bit of experience now," said Norrie. "It's a nice bonus, but there is a lot of tennis in the year to be played. It's a great achievement."

One man who will not qualify for the Finals is Aslan Karatsev. Last month's champion in Moscow lost in three sets to American Sebastian Korda, meaning he cannot now catch the top eight.

Rafael Nadal intends to make his Tour comeback next month and plans to play at the 2022 Australian Open.

The 20-time major champion has not played since a defeat to Lloyd Harris at the Citi Open in August.

The 35-year-old, who withdrew from Wimbledon and the Tokyo Olympics after losing to Novak Djokovic in the French Open semi-finals, also pulled out of the US Open due to a recurring foot injury.

Nadal has spent time training in Mallorca this month following treatment in Barcelona and said he was not sure when he would make his return to action.

Speaking at a sponsor event in Paris, Nadal said he hopes to play at the World Tennis Championship next month before a possible tilt at the first grand slam of next year, an event he has won just once back in 2009.

"My plan is to play Abu Dhabi in December and then in a tournament before Australia and then the Australian Open. That's my goal," Nadal said. "We're working hard to make it happen.

"The injury in my foot still needs to get a little better, but I'm already training almost an hour and a half a day so that's positive. Some days are better than others, but I'm starting to have a lot more positive days than negative ones.

"So, I'm on the right track. I'm training, I'm feeling better. I'm back on the court."

World number eight Casper Ruud and world number 13 Denis Shapovalov are two of the big names from the ATP Tour to have confirmed they will play in Abu Dhabi in the event that runs from December 16-18.

Women's Olympic gold medallist Belinda Bencic and surprise US Open champion Emma Raducanu have also signed up to make their tournament debuts.

The Australian Open, won this year by Novak Djokovic, is due to start on January 17.

Novak Djokovic is unwilling to commit to January's Australian Open as the defending champion awaits confirmation on travel and entry requirements amid Victoria's vaccine mandate.

The state of Victoria, where the year's opening grand slam takes place at Melbourne Park, has introduced a vaccine mandate for professional athletes and across most industries due to the coronavirus pandemic.

The 2021 Australian Open went ahead, albeit in February instead of January, and without fans for most of the tournament following a snap lockdown of Melbourne due to COVID-19.

Last week, Australia prime minister Scott Morrison said unvaccinated players would be allowed to contest the slam if they completed two weeks in quarantine, though Victoria premier Dan Andrews dismissed those comments, insisting athletes would not be granted access unless they received the COVID-19 vaccine.

A record nine-time Australian Open champion, world number one Djokovic remains non-committal over his looming title defence.

"Well, I'm going to decide on whether I go to Australia or not after I see the official statement from Tennis Australia," Djokovic said as he prepares for the Paris Masters – his first tournament since losing to Daniil Medvedev in September's US Open final.

"Right now, we don't have any official announcement or statement. So until that's out, I won't be talking about this anymore, because I don't want to be part of the stories about the assumptions and what-ifs.

"When official condition requirements to travel to Australia and play in Australia are out, then obviously I'll see what I personally do with that, and also the bigger group of the players, you know, because the situation is obviously different in Australia than most parts of the world."

World number two Medvedev also refused to confirm his Australian Open participation.

"I always said it, that I really like Novak's answer about this. I want to keep my medical, no matter if it's about vaccine, leg injury, head injury... I want to keep my medical private for a reason," Medvedev said.

"I feel like tennis is such a brutal sport where you're always one on one against your opponent, and any information you give him can go against you.

"If you're playing Australia, it's obvious you're vaccinated. So that's why I said I'm willing to play Australia, but I won't say if you'll see me there, but we're going to see in January."

World number one Novak Djokovic said he will return to action at the Paris Masters blessed to be a more "humble" tennis player.

The Serbian makes his first appearance since his US Open final defeat to Daniil Medvedev at the ATP 1000 tournament in the French capital.

That defeat in New York cost Djokovic the chance to become only the third man to win a singles calendar slam by winning all four majors in the same year.

Djokovic also missed the opportunity to move top of the all-time Grand Slam tournament winners list and remains joint-top alongside Roger Federer and Rafael Nadal with 20 titles.

However, the 34-year-old – whose status for the 2021 Australian Open remains unknown – was phlegmatic when he reflected on his loss to Russian world number two Medvedev.

"In a most ideal scenario, I would have won all four of them," Djokovic told a media conference. "Knowing I was so close gives me great encouragement for the future, but it also makes me feel humble about my game, about my career.

"It gives me a kind of reality check where I have to go back to the practice court and really understand what needs to be done so that I could improve.

"This was not an ordinary loss considering the circumstances. I have learned over the years to deal with losses in such way that I treat them as great opportunities for growth.

"I feel that the US Open loss in the final has arrived arguably at the worst or at the best time for me, in a way.

"I'm disappointed that I lost the match, but I feel like I was blessed to experience love from the crowd and support from the stadium that I have never experienced before in my life in New York, and actually not in many places around the world.

"That kind of energy that I received from the crowd from the moment I stepped on the court until I stepped out is a win for life."

Djokovic, who has won four of the last eight Paris Masters tournaments, claimed the prospect of ending the year as the world number one ahead of Medvedev will motivate him.

Should he do so then Djokovic would leapfrog Pete Sampras for the most year-end number one finishes in history with seven.

He will face either Italian Fabio Fognini or Hungarian Marton Fucsovics having received a bye through the first round.

"The year-end number one is on the line between Medvedev and myself, and I'm in a pretty good position," added Djokovic, who has won 85 ATP tour titles.

"That's obviously the goal for the end of the season other than trying to do well in the Davis Cup with the national team. So hopefully I can have a strong finish of the season and clinch that year-end number one.

"I’m pleased to be back. I have been training really well the past couple of weeks. And I have had plenty of success in Paris over the years, so that gives me enough reason to believe that I can do well.

"The lack of match play could be dangerous, so I have to really make sure that I start off my first match very well with a good intensity and build my form."

Marin Cilic won his 20th title on the ATP Tour by battling past Taylor Fritz in the final of the St Petersburg Open on Sunday.

A decade on from lifting the trophy for the first time, Cilic outlasted his American opponent 7-6 (7-3) 4-6 6-4 in a gruelling contest lasting two hours and 23 minutes.

It took the Croatian to four tournament wins on Russian soil, the 33-year-old having also twice won the crown in Moscow, while it also saw him join truly elite company in the men's game.

Only five other active male players have won 20 or more titles: Roger Federer (103), Rafael Nadal (88), Novak Djokovic (85), Andy Murray (46) and Juan Martin del Potro (22).

"Coming 10 years after winning in 2011 and also winning now, it's so, so special for me, especially this part of my career," said Cilic. "Having now a family, two sons, I want to absolutely dedicate this trophy to my newborn son."

Cilic had the chance to reach 20 titles last week in Moscow, only to lose in straight sets to home favourite Aslan Karatsev.

With 12 aces and 78 per cent of first-serve points won, the former world number three was aggressive in his efforts to make sure this was not another missed opportunity.

After taking the first set, Cilic twice led by a break in the second but allowed Fritz to level the contest and keep alive his hopes of a first title since Eastbourne two years ago.

Fritz went a break ahead in the decider but Cilic battled back to level at 4-4. A double fault from the world number 28 gave Cilic the chance to serve out the contest, and he duly obliged, converting his first match point with a volley.

Alexander Zverev captured his fifth title of the season at the Vienna Open after defeating Frances Tiafoe 7-5 6-4 in Sunday's final.

The Olympic champion claimed more silverware in Vienna, having also triumphed in Madrid, Cincinnati and Acapulco in 2021.

The world number four, who claimed his 300th tour-level career win against Alex de Minaur earlier in the week, is now 25-2 since exiting the fourth round at Wimbledon in July.

Tiafoe was appearing in his first ATP 500 final having defeated Stefanos Tsitsipas, Diego Schwartzman and Jannik Sinner along the way.

The world number 49 stuck with Zverev during a tight opening set, in which breaks were exchanged early on.

However, the German broke again in game 12 to draw first blood, and went on to hit eight aces during the second set.

Tiafoe produced an inspired turnaround from 5-2 down in the second set of his semi-final victory over Sinner.

But there was to be no fairytale finish for the American, who was seeking a second ATP title and first since the 2018 Delray Beach Open.

Zverev subsequently held his nerve to move level with Casper Ruud on five titles for the season, the most on the ATP Tour this year.

Frances Tiafoe will face Alexander Zverev in the Vienna Open final after storming back from the brink of defeat to beat Jannik Sinner.

Sinner was on the cusp of another final after his triumph in Antwerp last weekend when he led 5-2 in the second set, but qualifier Tiafoe roared back to win 3-6 7-5 6-2 on Saturday.

Italian Sinner had moved into the last qualifying position for the ATP Finals by beating Casper Ruud to reach the semi-finals in the Austrian capital and appeared destined to extending his winning run.

The 49-ranked Tiafoe had other ideas, winning five games in a row to force a deciding set.

Tiafoe maintained his momentum, breaking twice in the final set to complete an astonishing comeback and leave seventh seed Sinner shellshocked.

Second seed Zverev earlier marched into his fifth tour-level championship match of the season with a 6-3 6-3 defeat of Spanish teenager Carlos Alcaraz.

Zverev, who this week secured a 50th tour-level win of the season and a 300th of his career, needed only 68 minutes to knock Alcaraz out.

The German said: "I finally found my rhythm from the baseline because I was really struggling.

"I didn't feel the ball well and I spent some time on the court after the match yesterday and warmed up for an hour and a half before the match today and I finally got it."

Marin Cilic and Taylor Fritz will do battle in the St Petersburg Open final following contrasting wins over Botic Van de Zandschulp and Jan-Lennard Struff respectively.

Cilic did not face a break point in a 6-3 6-3 victory over Dutchman van de Zandschulp, while fought back to defeat Jan-Lennard Struff 5-7 6-1 6-3.

Top seed Andrey Rublev crashed out of the St Petersburg Open after a straight-sets defeat by Dutch qualifier Botic van de Zandschulp in the quarter-finals.

A recent US Open quarter-finalist, world number 69 Van de Zandschlup claimed the first top-10 win of his career on Friday.

The 26-year-old also advanced to the semi-finals of an ATP event for the first time.

There, he will face 2011 champion Marin Cilic, who was a 6-4 3-6 6-3 winner over third seed Roberto Bautista Agut.

Denis Shapovalov was another big-name casualty in Russia, the second seed going down 4-6 3-6 against world number 53 Jan-Lennard Struff.

Although, there were better fortunes for fifth seed Taylor Fritz. The Indian Wells semi-finalist is yet to drop a set this week after prevailing 6-4 6-2 against John Millman.

Elsewhere, Matteo Berrettini was the victim of another upset at the Erste Bank Open in Vienna.

The Wimbledon champion went down 1-6 7-6 (7-2) 6-7 (5-7) following a two-hour 40-minute battle with Carlos Alcaraz.

Reaching his first ATP 500 semi-final, the Spanish teenager claimed another big scalp having defeated Stefanos Tsitsipas at Flushing Meadows last month.

However, second seed Alexander Zverev remained on course for a fifth title of the season, as he claimed his 300th tour-level win.

The Australian Open finalist beat Felix Auger-Aliassime 6-4 3-6 6-3, avenging his fourth-round defeat by the Canadian at Wimbledon in July.

Alexander Zverev and Jannik Sinner moved into the quarter-finals of the Vienna Open on Thursday. 

Italian Sinner beat home hopeful Dennis Novak 6-4 6-2 to set up a tantalising showdown with Casper Ruud. 

Should he win that match, Sinner will move ahead of Hubert Hurkacz in the race to qualify for this year's ATP Finals, while victory for Ruud will strengthen the Norwegian's standing. 

"It's going to be tricky," said Sinner. "He's in a better position than I am for the race. I think right now it's tough to say and tough to do because in the end you try always not to think about that, but in the end you think about that because you believe." 

Zverev was given a sterner test, eventually overcoming Alex de Minaur 6-2 3-6 6-2 in one hour and 42 minutes. The Olympic gold medallist will now face Felix Auger-Aliassime, who fought back from a set down to defeat Cameron Norrie. 

Frances Tiafoe came from a set down to upset top seed Stefanos Tsitsipas 3-6 6-3 6-4 and earn a quarter-final meeting with Diego Schwartzman after the Argentine overcame Gael Monfils 7-6 (7-5) 4-6 6-2. 

In St Petersburg, home favourite and sixth seed Karen Khachanov lost a gruelling three-set encounter to Marin Cilic. 

The Croatian, who won the title in Russia in his last appearance in 2011, was 4-1 down in the deciding set but took all five of the final games to triumph after two and a half hours on court. 

"Everybody is playing good. The tournament is great. It's the end of the season, so everybody wants to finish on a great level," said Cilic, who next faces Roberto Bautista Agut. "For me, it was great to play this kind of a match today." 

Another Russian, Aslan Karatsev, fell to John Millman 6-3 6-2. Taylor Fritz and Botic van de Zandschulp also progressed in straight sets. 

Jannik Sinner continued his push for an ATP Finals spot with a straight-sets defeat of Reilly Opelka in the first round of the Vienna Open, while Carlos Alcaraz exacted revenge on Andy Murray.

Sinner won his fourth title of what has been an outstanding season for the Italian in Antwerp last weekend and is only 110 points adrift of Hubert Hurkacz in the battle for the final place in the season-ending event in Turin.

Murray did the 20-year-old a favour by knocking Hurkacz out of the ATP 500 tournament in the Austrian capital on Monday and seventh seed Sinner eased to a 6-4 6-2 win over American Opelka two days later.

Sinner, who will overtake Pole Hurkacz if he reaches the semi-finals this week, won 93 per cent of points behind his first serve and did not face a break point in a resounding win and will play Dennis Novak in the second round.

Murray beat Alcaraz at Indian Wells this month, but the 18-year-old rising star from Spain turned the tables on the three-time grand slam champion with a 6-3 6-4 second-round win in Vienna.

Former world number one Murray struggled with his serve and was broken five times as he made an early exit.

Third seed Matteo Berrettini beat Nikoloz Basilashvili 6-7 (5-7) 6-2 6-3 to reach the third round, while Diego Schwartzman, Gael Monfils and Lorenzo Sonego moved into the second round.

In the St Petersburg Open, defending champion Andrey Rublev beat Ilya Ivashka 6-4 6-4 to reach the quarter-finals along with Denis Shapovalov, a 2-6 6-3 6-0 winner against Pablo Andujar.

Jan-Lennard Struff also moved into the last eight, with Karen Khachanov and Marin Cilic securing first-round wins.