The 6-2 6-2 win in Umag meant 18-year-old Alcaraz became the youngest tour-level champion since Kei Nishikori won at Delray Beach in 2008, also aged 18.
Despite his tender years, seventh seed Alcaraz was too hot to handle for Gasquet, the highly rated Spaniard cruising past his significantly more experienced opponent in one hour and 17 minutes.
"I had a lot of good moments in this tournament. I beat five great tennis players," Alcaraz told atptour.com.
"I think that I grew up a lot in this tournament and I keep a lot of experience from this tournament. It's going to be useful for the future."
Gasquet, who needed more than three hours to overcome Daniel Altmaier in the last four, was hoping to win his first tour title since 's-Hertogenbosch in 2018.
"It was tough for me to play [with] full intensity. I had a tough match yesterday. It was tough, and especially with a guy like Carlos, who is playing really fast with a lot of energy and spin," Gasquet said.
"He’s playing unbelievable. He’s only 18 and of course he has a great future and I just couldn’t play at his level and his intensity.
"That was the key of the match and he didn't lose a point. He played well, very solid. He's a great player."
The highly rated Spanish teenager eventually downed the German wildcard 3-6 6-1 7-6 (7-3).
Kuhn, ranked 259 in the world, was aggressive early on against Alcaraz, and was rewarded with the first set.
But the 19-year-old – playing as top seed in an ATP Tour event for the first time – rallied to ease through the second set, before being made to work much harder to clinch the win on a tie-break.
Alcaraz will now play Filip Krajinovic in the second round after the Serbian also won in a third-set tie-break against Sebastian Baez 6-1 4-6 7-6 (8-6).
Three seeded players crashed out on Tuesday in straight sets, with third favourite Diego Schwartzman losing against Emil Ruusuvuori 7-5 6-4, sixth seed Nikoloz Basilashvili beaten by Aslan Karatsev 6-4 6-0, and eighth seed Holger Rune going down 7-6 (10-8) 7-5 to Tallon Griekspoor.
Fourth seed Pablo Carreno Busta eased through against Luca Nardi 6-2 6-1, while there were also wins for Fabio Fognini, who sealed his 400th career victory, as well as Daniel Elahi Galan, Borna Coric and Francisco Cerundolo.
At the Swiss Open in Gstaad, sixth seed Cristian Garin lost 6-3 6-4 to Yannick Hanfmann and seventh favourite Hugo Gaston fell to Dominic Thiem despite winning the first set, losing 1-6 6-1 7-6 (9-7).
Elsewhere, Frenchman Richard Gasquet beat Roberto Carballes Baena 7-5 6-4, while his compatriot Benoit Paire retired hurt when a set and a break down against Elias Ymer.
A tight game between Swiss pair Dominic Stricker and Marc-Andrea Huesler saw the former prevail 6-7 (2-7) 7-6 (7-2) 6-4, and an all-Spanish affair was similarly close as Jaume Munar defeated Bernabe Zapata Miralles 6-3 3-6 7-5.
There were also wins for qualifiers Juan Pablo Varillas and Nicolas Jarry against Lorenzo Sonego and Thiago Monteiro respectively.
2017 runner-up Joao Sousa cruised past Vit Kopriva 6-1 7-5 and Jurij Rodionov set up a Round of 16 meeting with third seed Roberto Bautista Agut with a straight-sets victory over Hernan Casanova.
Dominic Thiem, who won the 2019 edition of the competition, will face Alexander Shevchenko tomorrow while Richard Gasquet will take on Sebastian Ofner.
2016 Croatia Open winner Fabio Fognini will not be regaining his title in Umag this year, after the seventh seed was knocked out by Colombian Daniel Galan in a 3-6 7-5 3-6 defeat.
Galan will play Giulio Zeppieri in the next round, who came from one set down to overcome world number 90 Pedro Cachin 3-6 6-1 6-4.
Fifth seed Alex Molcan plays his first game tomorrow against Duje Adjukovic, and sixth seed Daniel Altmaier will take on French 23-year-old Corentin Moutet.
Former Wimbledon runner-up Berrettini beat American Mackenzie McDonald 3-6 7-6 (7-2) 6-3 at the hard court event, while Musetti came through 6-3 6-4 against Serbian Miomir Kecmanovic.
Providing Berrettini is healthy to participate in the final, the tournament looks set to deliver a crowd-pleasing trophy match, but it was touch and go whether the Rome native would get through the McDonald match.
"I don't even know how I did it," Berrettini said. "I wasn't feeling very good. I asked for the physio because my foot was hurting. It happened so many times in my career that I had to fight through so many things, not just thinking about the tennis ball."
He added, quoted by the ATP: "I didn't want to retire. My team told me, 'I think you should stop'. But I tried and I found a way."
Berrettini and Musetti have never gone head-to-head before. Berrettini has won two titles this year, both on grass, in Stuttgart and at London's Queen's Club, while 20-year-old Musetti scooped his maiden ATP title on clay in Hamburg.
At the European Open in Antwerp, Sunday's final will see American Sebastian Korda tackle Canadian Felix Auger-Aliassime, in a battle of two in-form players.
Korda was runner-up last week in Gijon, while Auger-Aliassime took the title in Florence, adding to his Rotterdam triumph from February.
Korda wrestled his way past a recently resurgent Dominic Thiem, scraping a 6-7 (4-7) 6-3 7-6 (7-4) victory, before Auger-Aliassime was given a mighty battle by veteran Frenchman Richard Gasquet, winning through in two tight sets, 7-6 (7-2) 7-6 (7-3) his margin.
Like Berrettini and Auger-Aliassime, Greece's Stefanos Tsitsipas has a third title of the year in his sights this weekend.
Tsitsipas swept through to the final of the Stockholm Open with a 6-2 6-2 win over Finland's Emil Ruusuvuori, setting up a clash with 19-year-old Danish player Holger Rune.
For Rune, there was no such straightforward path into the final as Alex de Minaur pushed him all the way, with the Australian eventually edged out 4-6 7-6 (7-1) 7-5 after two hours and 50 minutes.
The 2016 champion, Carreno Busta had his sights set on the semi-finals of the ATP 250 tournament but he suffered a surprise 7-6 (7-2) 6-3 loss on Thursday.
"Of course it's a great feeling. I had a great match today. These conditions suit me," Ivashka said. "I think he had more pressure because he's the top seed so for me it was a good challenge to see what my level is and to compete with these guys, so for me it was a great match."
Carreno Busta – who trumped world number one and 20-time grand slam champion Novak Djokovic to win bronze at the Olympic Games – was not the only seed to fall.
Richard Gasquet and Frances Tiafoe also crashed out in the quarter-finals following defeats to Emil Ruusuvuori and Mikael Ymer.
The only seed to advance to the semis was 15th seed Carlos Alcaraz, who saw off Marcos Giron.
World number 16 Carreno Busta, the seventh seed at the ATP 500 event in the Netherlands, took the first set with ease but fell to a 2-6 7-6 (7-2) 6-2 defeat against Frenchman Gasquet.
Veteran Gasquet, ranked 45th in the world, will next meet Stan Wawrinka after the Swiss overcame Alexander Bublik in dominant fashion with a 7-6 (7-5) 6-4 triumph.
Grigor Dimitrov recorded a 6-1 6-3 victory over Aslan Karatsev in just 59 minutes to set up a potential second-round tie with fifth seed Hubert Hurkacz, who must first get past Roberto Bautista Agut.
Qualifier Gregoire Barrere was another straight-sets winner, defeating David Goffin 6-0 7-6 (7-3).
The Frenchman, who is ranked 71st in the world, could meet third seed Felix Auger-Aliassime in the next round if the Canadian overcomes Italy's Lorenzo Sonego.
Carreno Busta – the 2016 champion – was too good for Dominik Koepfer 6-2 6-3 at the ATP 250 tournament on Wednesday.
The Spaniard, who stunned world number one Novak Djokovic to win bronze at the Olympic Games, will meet Ilya Ivashka, who upstaged ninth seed Jan-Lennard Struff 6-2 6-1.
"It was a very good match. I think I played very aggressively today, I made a lot of winners," Carreno Busta said. "I played against him the last two tournaments so it was important to me at the beginning of the match to be very focused and play very aggressive so I think this was a very good match for me.
"I'm feeling really comfortable playing this year, also. We know next we have the US Open but day by day I need the confidence, I need the rhythm. I think that I'm playing at a really good level so I would like to continue this way."
Former world number seven Richard Gasquet saw off third seed Daniel Evans 6-4 7-6 (7-4), Frances Tiafoe defeated Thiago Monteiro 7-5 7-6 (7-2), while fourth seed Marton Fucsovics was sent packing by Carlos Alcaraz 6-3 0-6 6-2.
Rinderknech, who sits 65th in the world rankings, had not recorded a Tour-level victory before 2021 but has now triumphed 15 times after cruising past Delbonis 6-4 6-4.
The Frenchman will meet eighth seed Dusan Lajovic in the second round in Antwerp, after the Serbian downed Richard Gasquet 7-6 (7-3) 6-1 on Monday.
The other first-round clash in Belgium saw Alexei Popyrin capitulate in the third set as he succumbed to a 4-6 6-3 0-6 defeat against world number 62 Botic van de Zandschulp.
Americans Jenson Brooksby and Brandon Nakashima also booked their places in the main draw. Brooksby defeated Norbert Gombos 6-4 6-2, while Nakashima overcame Pierre-Hugues Herbert 6-2 6-4.
Meanwhile in Russia, Cilic – who has claimed the crown in Moscow twice previously – recovered from a first-set scare in his round-of-32 tie with qualifier Damir Dzumhur, eventually triumphing 6-7 (4-7) 6-1 6-1.
John Millman experienced similar difficulties, with Benjamin Bonzi claiming the first set before the Australian succeeded 6-7 (5-7) 6-4 6-3 to set up a potential second-round match against fifth seed Alexander Bublik.
De Minaur, the ninth seed in Dubai, won his first tournament of 2021 in Antalya in January.
However, the Australian's results since then have rapidly declined and his latest loss - 2-6 6-3 6-4 to Chardy - means he is 3-5 since his title in Turkey.
De Minaur seized his first two break points against Chardy, yet the next four came and went while his opponent proved clinical, taking his only two opportunities and snatching victory.
The Frenchman, who reached the semi-finals in Antalya and again at an ATP 250 event in Melbourne prior to the Australian Open, said: "I've played good since the beginning of the year.
"It is always easier to play when you are confident. If you play a bad set, it is never finished. I stayed focused and tried to find a solution."
It was not a successful start to the week for De Minaur's compatriots either, as John Millman was among three other Aussies to crash out.
Christopher O'Connell missed the chance to set up a meeting with Dominic Thiem as Lloyd Harris advanced, and qualifier Emil Ruusuvuori saw off Jordan Thompson ahead of facing Andrey Rublev.
Marton Fucsovics was back in action after handing a walkover to Rublev, the same man who had previously beaten him to the Rotterdam Open title, in Qatar last week.
He defeated Vasek Pospisil in three sets, while there was a milestone win for Richard Gasquet, another man unable to line up against Rublev in Doha.
A 6-4 6-2 win over Marco Cecchinato was his 550th on the ATP Tour, making him only the sixth active player to that mark after the 'big four' of Roger Federer (1,243), Rafael Nadal (1,008), Novak Djokovic (943) and Andy Murray (677) and Spain's Fernando Verdasco (552).
"I am feeling great here," Gasquet said. "I know this court well. I played well last year. It is a fast court. I like to play on it.
"It is important to serve well and it was a great match. I started well, feeling confident and winning the first set, and then I played better in the second set."
For Djokovic, a 10th win in a row came in an absorbing battle with his Paris-born American opponent Maxime Cressy, who displayed a typically aggressive approach on serve, with 15 aces and 10 double faults overall.
Djokovic was strong on his own delivery, however, with the Serbian losing just six points on serve and not facing a break point on his way to a 7-6 (7-1) 6-4 victory.
"I'm happy with the way I played," Djokovic said. "When chances were presented, I was able to use them, even though I did have some missed break points.
"But it was very challenging, first match with a guy who serves extremely well and strong and fast.
"He's comfortable coming to the net. It's nice to see. I think he's the only guy that really comes to the net after every first and second serve. I think it's good for tennis to see that, particularly in these modern times when most of the players are playing from back of the court. He's a very athletic guy.
"It's difficult to play him definitely in these kind of conditions where balls are flying through the court and it's quicker than it was last year. So tough to break.
"But I didn't make too many unforced errors. I'm very pleased with the way I served, with the way I was holding my service games. Just the way I felt, the way I played, it was all positive."
Third seed Ruud ground out a 6-1 7-6 (9-7) victory against Frenchman Richard Gasquet, with the Norwegian saving three of four break points in what proved to be a tightly fought contest.
Mistakes from Gasquet were ultimately costly, the veteran having 10 unforced errors in the second set compared to Ruud's two.
Seventh seed Andrey Rublev was also victorious, the Russian winning 6-2 6-3 against American John Isner, while the British duo of Jack Draper and Dan Evans progressed to the last-32 stage, beating Arthur Rinderknech and Brandon Nakashima respectively.
Federer, 41, won the first of his grand slams in 2003 at Wimbledon, and in that tournament it was Hewitt who was the reigning champion after becoming the youngest ever world number one back in 2001.
They came through in the same era, with Federer quickly overtaking the Australian as the sport's top attraction, and he would retain that mantle for over a decade as he and Rafael Nadal began their legendary rivalry.
Reflecting on their time on tour together, Hewitt called him "nearly unbeatable" as he shared his admiration.
"Yeah, he was from my kind of era, I guess," he said. "We were the same age, we grew up together in juniors.
"I knew Roger extremely well and probably saw him slightly different to everyone else as well, because we grew up together. But he was the greatest of that time.
"You know, obviously there are a couple of other guys now that are really putting their hand up, but he went clear easily from a grand slam perspective and really just his win-loss ratio [in the] mid-2000s era, he was nearly unbeatable.
"It was pretty much only Rafa [Nadal] that could get him, especially on the clay. But most of all he's been a great ambassador for our sport.
"I've always said that you don't want to push those guys out of the game too early.
"Everyone wants to talk about retirement. When are they going to retire? You want to hold on to those greats. They've done so many special things for our sport.
"But yeah, obviously, the body – you get to my age and his age now, and it's not easy. He's done everything in the sport that you could ever dream of."
In his own interview, Gasquet shared the sentiment, declaring "there is only one Roger Federer".
"It is a big shock – he is a legend of the game," he said. "It's not easy for anybody, I know it will be a big thing at the Laver Cup. I'm sure it will be wonderful there.
"It's a tough loss for tennis. It will be different after that. It's still tennis, but it won't be the same without Federer.
"I was leading 1-0 against him [head-to-head], I won in Monte Carlo – but after that I lost maybe 20 times. I'm not the only one of course, it was incredible when I got to face him.
"He is a legend of the game, everybody knows it. The technique, the charisma – everything was crazy. There is only one Roger Federer."
Thiem will retire later this year due to a persistent wrist injury that has derailed his career but will likely need to battle through the qualifying rounds to appear at Roland Garros for a final time.
The two-time French Open semi-finalist is currently six places away from a main-draw spot for the upcoming major, with Richard Gasquet among the eight male players to secure a wild-card invitation.
Frenchman Gasquet will equal Feliciano Lopez's 21 tournaments at Roland Garros, the joint-most appearances of any player in the Open Era.
In the women's tournament, world number 99 Alize Cornet was also invited on a wild-card pick and will appear in a women's singles grand slam main draw for the 72nd time in her career.
That is the third most in the Open Era for major appearances, behind only Venus Williams (93) and Serena Williams (81).
Gasquet, the final French player in either the men's or women's draws, offered some resistance after a terrible start but succumbed 6-0 7-5 6-2 in two hours and 14 minutes.
Nadal has now beaten Gasquet in all 17 of their meetings on Tour, with the Frenchman falling to a Spaniard for the second tournament running, having lost 6-1 6-1 to Jaume Munar in Parma last month.
The 20-time major singles champion turned 35 on Thursday and seemed eager to go and enjoy what remained of his birthday as he reeled off the first seven games in a row inside half an hour.
Gasquet at last got on the board after a couple of strangely errant forehands from the defending champion, who broke Gasquet again at the third time of asking as he moved 4-1 ahead in the second set.
Gasquet might have dropped to 53 in the rankings, but he offered glimpses of the form that saw him climb as high as seven in the world back in 2008, the one-handed backhand and drop-shot game causing Nadal some problems.
There was a shock when he broke back at 4-5 behind in the second set as Nadal looped another forehand long, but Nadal piled on the pressure at 6-5 and took a 2-0 lead when Gasquet slapped a forehand into the bottom of the net.
A sublime volley and a rasping passing shot saw Gasquet fend off two more break points at 1-2 in the third, but his resistance was finally broken in a mammoth sixth game.
Gasquet's serve deserted him at the wrong moment as he handed Nadal two match points, the second of which was taken via another forehand into the net.
Data Slam: Nadal keeps Gasquet at arm's length
Nadal dropped just seven of 45 points behind his first serve, which averaged speeds of 180km/h, leaving Gasquet with few opportunities to knock the Spaniard off his game.
Such authority meant Gasquet had little chance of snapping his losing streak against Nadal, whose 17 wins from 17 meetings is a career record.
WINNERS/UNFORCED ERRORS
Nadal – 36/23
Gasquet – 20/37
ACES/DOUBLE FAULTS
Nadal – 3/3
Gasquet – 2/5
BREAK POINTS WON
Nadal – 7/16
Gasquet – 1/4
Pouille was on the brink of elimination in qualifying after facing match point before booking his spot in the main draw.
Now, the Frenchman is preparing for the second round following his 6-1 6-4 victory over Lopez on Monday.
Pouille saved all four break points he faced as the former world number 10 claimed his first ATP Tour-level victory since April's Monte Carlo Masters.
Awaiting Pouille in the second round is third seed Daniel Evans, who received a bye in the opening round.
As for 14th seed Richard Gasquet, he prevailed 7-6 (7-4) 7-6 (8-6) against Egor Gerasimov at the ATP 250 event.
Elsewhere, Federico Coria and Jordan Thompson were among the players to progress.
The biggest names in the field learned their opponents after the 32 seeded entrant received byes into the second round of the Masters 1000 event, and Tsitsipas will be desperate to avoid a third consecutive loss after quick exits at the Rotterdam Open and Indian Wells Open in recent weeks.
Fourth seed Daniil Medvedev is waiting for Roberto Carbellas Baena after he blew away Bernabe Zapata Miralles 6-0 3-0 (retired) in an all-Spanish showdown, while fifth seed Felix Auger-Aliassime will meet Brazil's Thiago Monteiro in the second round after his 6-4 7-6 (8-6) triumph over Australia's Jason Kubler.
After O'Connell and Kubler both fell, Thanasi Kokkinakis flew the flag for Australia with a 4-6 6-3 7-6 (9-7) comeback against Belgian wildcard Zizou Bergs, and his reward will be a battle against Polish eighth seed Hubert Hurkacz.
France's Gregoire Barrere earned a big matchup against 11th seed Cameron Norrie after eliminating Roman Safiullin 6-4 3-6 6-3, and Safiullin's Russian compatriot Pavel Kotov will join him on an early flight home after going down 6-2 6-2 against recent Chile Open finalist Tomas Martin Etcheverry.
Gasquet – three times a champion in Montpellier and once in Lyon – needed just 87 minutes to overcome Simon in his first-round match on Wednesday and set up a last-16 tie against Feliciano Lopez, who beat eighth seed Ugo Humbert.
The other first-round match saw Adrian Mannarino defeat Alexei Popyrin and progress to face top seed Gael Monfils.
Two last-16 matches also took place, with world number 23 Grigor Dimitrov, who entered as a wildcard and was seeded fourth, going down 6-7 (4-7) 6-4 7-5 to Gregoire Barrere.
Third seed Denis Shapovalov also suffered a quick exit as he lost to Vasek Pospisil 6-2 6-3.
Meanwhile, at the Pune Open, second seed Ricardas Berankis saved two set points as he rallied to defeat Cedrik-Marcel Stebe 7-6 (7-2) 6-1.
World number 73 Berankis will go up against Yuichi Sugita, who progressed without playing after Viktor Troicki withdrew due to fever, in the quarter-finals. Jiri Vesely and Ilya Ivashka also progressed.
Norrie grew up in Auckland, and the British number one reached his first ATP Tour-level final in the city in 2019.
But despite repeating that feat and then winning the opening set of Saturday's final, Frenchman Gasquet roared back to lift his first title on the ATP Tour since 2018.
After they split the opening two sets, Norrie looked to be on the way to victory when he held a 4-1 lead in the decider.
But 36-year-old Gasquet rattled off five straight sets, including two breaks of serve, to shock the second seed and become the oldest champion in the Auckland Open's 66-year history.
"It's an amazing title for me, especially now at my age," Gasquet told a post-match news conference. "I really didn't think I would win again.
"I'm 37 this year, so when I came here last week, if you were to tell me next Saturday you will win here, I wouldn't believe it."
Norrie gets his Australian Open campaign underway against wildcard Luca van Assche on Monday, while Gasquet will play fellow Frenchman Ugo Humbert in the first round.
At the Adelaide International 2, Kwon Son-woo defeated Roberto Bautista Agut 6-4 3-6 7-6 (7-4) to take the crown.
Bautista Agut, who knocked out defending champion Thanasi Kokkinakis in the semi-finals, hit back from losing the opening set to level the game with a strong second stanza.
The deciding set went all the way to a tie-break as both players lost two of their service games, but with Kwon 5-4 up in the pivotal tie-break, the world number 84 found two breaks of serve to complete the victory.
The win was Kwon's second ATP Tour title and first since lifting the Astana Open trophy in 2021, while he becomes the first South Korean to win multiple Tour-level titles.
World number 10 Goffin has started the season in impressive form and remains on course for a first ATP Tour title since Tokyo in 2017.
The second seed bested Bublik's varied strokeplay over the course of one hour and 47 minutes, with the 22-year-old even serving underarm in a bid to deceive Goffin as a gripping second-set tie break slipped away.
Goffin will face Pierre-Hugues Herbert in the quarter-finals after the home favourite claimed an impressive 7-6 (7-2) 7-5 triumph against Felix Auger-Aliassime.
Herbert was a finalist in Montpellier last year, while countryman Richard Gasquet remained in contention for his fourth win at the event by beating Feliciano Lopez 6-7 (1-7) 6-4 6-2.
Vasek Pospisil, a winner in the all-Canadian clash with Denis Shapovalov on Wednesday, is up next for Gasquet, who retained his place in a draw stacked with French hopes.
Gael Monfils came from a set down to beat compatriot Adrian Mannarino 4-6 6-1 6-4, joining Gregoire Barrere – a shock winner over Grigor Dimitrov a day ago - in the last eight.
Filip Krajinovic will be Barrere's next opponent after demolishing qualifier Mikael Ymer 6-1 6-1, with Norbert Gombos also seeing off Emil Ruusuvuori in straight sets.
At the Pune Open, top seed Benoit Paire was dumped out in straight sets by Roberto Marcora – the Italian qualifier prevailing 6-4 6-4.
Elsewhere, seeds Ricardas Berankis, Kwon Soon-woo, Yuichi Sugita, James Duckworth and Egor Gerasimov emerged unscathed to reach the quarter-finals.
Rune was beaten by Marc-Andrea Huesler in the final of the last tournament he entered in Sofia following a quarter-final appearance in Metz.
The Danish teenager, who last week announced Patrick Mouratoglou had joined his team for the rest of this season, defeated Monteiro 7-5 6-2 on his debut in the Swedish capital.
Rune did not face a break point and won 86 per cent of points on his first serve as he booked a meeting with Cristian Garin.
Garin beat qualifier Jason Kubler 6-2 6-4, while Maxime Cressy and Aslan Karatsev advanced to the last 16 at the expense of Ilya Ivashka and Lukas Rosol respectively.
Richard Gasquet consigned Stan Wawrinka to an early exit at the European Open, coming from a set down to win 2-6 7-6 (7-4) 6-4 in a battle of two of the most experienced players on the circuit.
Fifth seed Dan Evans beat Tallon Griekspoor 6-3 6-4 in the first round in Antwerp, while his fellow Brit Jack Draper was an emphatic 6-1 6-2 winner against Jenson Brooksby of the United States.
World number two Medvedev was making his first appearance since March after undergoing a hernia operation and fell to a 6-2 7-6 (7-5) defeat.
The Russian's rustiness was clear in the last-16 tussle as he racked up seven double faults and struggled to make inroads on Gasquet's second serve, with the Frenchman winning 61 per cent of points behind it.
It was the first time Gasquet overcame an opponent ranked in the top two since beating Roger Federer at the 2005 Monte Carlo Masters.
Next up for Gasquet will be Kamil Majchrzak, who beat Marco Cecchinato 6-2 6-3.
At the last-32 stage, Fabio Fognini went down 6-4 6-3 to Thanasi Kokkinakis and Albert Ramos-Vinolas succumbed to a 7-6 (7-5) 6-4 loss against Christopher O'Connell.
Johan Nikles, Nikoloz Basilashvili and Joao Sousa also advanced to the second round.
Top seed Cameron Norrie cruised into the quarter-finals of the Lyon Open by beating Francisco Cerundolo 6-4 6-4.
The Briton will face another Argentinian next in the form of Sebastian Baez, who came from a set down to beat Oscar Otte 5-7 6-4 6-2.
Alex De Minaur also had to rally for a 1-6 6-3 6-2 win against Ugo Humbert, with Yosuke Watanuki awaiting in the last eight after the world number 263 beat Soonwoo Kwon 6-3 6-4.
