Top seed Dominic Thiem was beaten in straight sets in the second round of the Dubai Tennis Championships by Lloyd Harris.

The reigning US Open champion, given a bye for the first round, lost 6-3 6-4 to his South African opponent, who sits 77 places further down the ATP rankings.

The Austrian has endured a difficult start to 2021. He lost in straight sets to Grigor Dimitrov in the last 16 of the Australian Open and was beaten by Roberto Bautista Agut in the quarter-finals in Doha.

It was a first win over a top-five player for Harris, who was not once taken to deuce on serve during their 72 minutes on court.

"I'm super, super happy with that win. [He is] by far the highest-ranked player I have beat," said Harris. "I look up to Domi a lot so, for me, it is a special feeling. I am really happy. Just the fact that I am playing good tennis, match in, match out now is giving me a lot of confidence.

"I was serving really well. I don't think I faced any break points. I took control of those games and [in] one or two games on his serve, I gave myself a good look. I played some of the important points very well. I am very proud of that."

While Thiem is struggling for form, things are looking far better for Andrey Rublev, who beat Emil Ruusuvuori 6-4 6-4 to stretch his winning streak at ATP 500 events to 21 matches.

The world number eight, who will face Taylor Fritz in the next round, equalled Andy Murray for the second-best winning run at this level of the Tour. Roger Federer (28) holds the record.

Third seed Denis Shapovalov beat Jan-Lennard Struff for the loss of just four games, while Bautista-Agut advanced after opponent Matthew Ebden retired in the first set.

Fifth seed David Goffin was beaten in straight sets by Kei Nishikori, who recorded just his third victory of the year.

Karen Khachanov and Jannik Sinner each advanced after three-setters, while Marton Fucsovics and Aslan Karatsev were also taken the distance before progressing.

Hubert Hurkacz, Lorenzo Sonego, Dusan Lajovic, Aljaz Bedene and Filip Krajinovic also won on Tuesday.

Alex de Minaur's tough run of form continued as he let a set lead slip to lose to Jeremy Chardy at the Dubai Tennis Championships on Monday.

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."

Garbine Muguruza reached the final of the Dubai Tennis Championships after a gruelling victory over Elise Mertens on Friday.

The Spaniard saw six match points come and go in a battle lasting two hours and seven minutes before eventually closing out a 6-4 7-6 (7-5) win.

Having reached the final in Doha last week, where she lost to Petra Kvitova, Muguruza is the fifth player this century to reach back-to-back finals in the Middle East double, after Martina Hingis, Justine Henin, Caroline Wozniacki and Svetlana Kuznetsova.

The two-time major winner has now reached three finals in her past four tournaments and has won 17 matches in 2021.

Despite being ahead for much of the match, Muguruza was nonetheless pushed hard by Mertens, who fought back to beat Jessica Pegula in the quarter-finals after facing three match points.

She led by a set and 5-3 but Mertens continued to come up clutch at key points until Muguruza at last completed the job with a smash in the tie-break.

"You have to be all the time concentrated, otherwise she will come back," she said. "I didn't lose the focus even though I couldn't close it [at first] – I was just looking forward to the next opportunity.

"I didn't think I played bad on the match points. They were just tough points that didn't come to my side. She was very good in defence and on those points, I felt she brought her magic. But I was like, 'Okay, I'm playing well, sooner or later I will convert the match point'. I didn't lose the concentration or get too irritated."

Muguruza will face Barbora Krejcikova in the final, the Czech defeating Jil Teichmann 7-5 6-2.

Krejcikova saved 10 of 11 break points as she reached just the second Tour final of her singles career and has yet to drop a set at this tournament.

The world number 63 is the lowest-ranked singles finalist in history in Dubai, with that previous record held by Virginie Razzano, who was ranked 58 in the world when she lost to Venus Williams in 2009.

Elise Mertens came from behind to clinch a semi-final spot at the Dubai Tennis Championships but Coco Gauff bowed out on Thursday.

Mertens said she "just didn't want to let go" after coming back from the brink to end Jessica Pegula's fine run with a 5-7 7-5 6-0 victory.

The Belgian looked to be heading out when she faced a 5-2 deficit in the second set, yet saved three match points to force a decider.

"I kept on fighting and that was the spirit today," said world number 18 Mertens.

Former world number one Muguruza is Mertens' semi-final opponent, the Spaniard having come from a set down to beat third seed Aryna Sabalenka 3-6 6-3 6-2.

Muguruza lost out to Petra Kvitova in the final of the Qatar Open last week, but looks on top form as she closes in on another championship match.

Sabalenka fell foul of Muguruza in Doha, and the Belarusian was unable to gain revenge as the ninth seed earned a 16th win of the season.

There was to be no place in the last four for 16-year-old Gauff, who came up short against world number 54 Jil Teichmann.

Gauff, who defeated Teichmann twice in Australia in February, was broken to go 5-3 down in the first set and could not respond.

A second break in Teichmann's favour put Gauff on the back foot in the second, and the Swiss then saved three break points to nose into a 3-1 lead.

The contest was settled on Gauff's serve – Teichmann taking the match at the second time of asking to tee up a last-four clash with Barbora Krejcikova, who beat Anastasia Potapova 6-0 6-2 in a little over an hour.

Krejcikova was beaten in the doubles final last year, and has claimed her place in the singles semi-finals of a WTA 1000 event for the first time.

Rafael Nadal has turned down a wildcard invitation to compete in next week's Dubai Tennis Championships as he does not feel ready to return to action.

The world number two has been struggling with a lower back injury sustained prior to the Australian Open, which he exited in the quarter-finals at the hands of Stefanos Tsitsipas.

Nadal has not competed since, having subsequently pulled out of the ATP Cup and Rotterdam Open after being advised to give his back time to heal.

And the 20-time grand slam winner will delay his return for a little while longer after deciding to skip the upcoming ATP 500 event in Dubai.

"I would like to thank the @DDFTennis for the wild card invitation sent to me," Nadal posted on his Twitter page on Thursday. 

"We seriously thought about coming to play, but I don't think I am ready to play yet. Once again thanks to the tournament's kind invitation and best of luck with the tournament."

The Spaniard added in a later tweet: "And special thanks to Tournament Director Salah Talak since I am aware of his efforts to ensure a smooth arrival to play Dubai during this unprecedented Coronavirus pandemic and difficult times for all."

Nadal won his only Dubai Tennis Championships title in 2006 with victory over Roger Federer – the competition's record eight-time winner – in the final.

Federer is scheduled to take part in this year's tournament after making his long-awaiting return from a 14-month injury lay-off at the Qatar Open this week.

Garbine Muguruza made light work of Iga Swiatek to book her place in the quarter-finals of the Dubai Tennis Championships.

The in-form Spaniard required just one hour and nine minutes to win 6-0 6-4 against the number eight seed and reach the final eight for the fourth time in seven appearances at the tournament.

Reigning French Open champion Swiatek came into the contest on a six-match winning streak but her resistance seemed to falter after she dropped serve in the opening game and then failed to capitalise on two break points in the second.

Muguruza, whose 2021 record now stands at 15 wins and four defeats, was comparatively ruthless against an opponent who landed with just 38 per cent of her first serves.

The former world number one and double grand-slam champion let a 3-1 lead slip in the second set before resuming control through her punishing forehand, getting the job done on the first match point with an ace.

She will be back into action on Thursday against Aryna Sabalenka. The Belarusian, who beat Anett Kontaveit 6-3 6-2, lost in three sets to Muguruza at the Qatar Open last week.

"Back-to-back matches is good," said Muguruza. "That means I'm playing the top players, that means I'm getting into the deep rounds. I'm looking forward for another battle."

Coco Gauff reached the last eight of a WTA 1000 event for the first time after a straight-sets win over qualifier Tereza Martincova.

The American, who turns 17 on the day of the final, won 6-4 6-2 to set up a showdown with Jil Teichmann, a 6-3 6-3 winner over Ons Jabeur.

Second seed Karolina Pliskova was a surprise casualty, losing in less than an hour to Jessica Pegula. The world number 36, who also beat Pliskova in Qatar, will face Elise Mertens after she beat Caroline Garcia 6-4 6-2.

The last remaining former champion in the draw, Belinda Bencic, suffered disappointment on her 24th birthday as she lost 6-1 2-6 7-5 to wildcard Anastasia Potapova. She will take on Barbora Krejcikova, who eliminated Svetlana Kuznetsova.

Elena Rybakina, the 2020 finalist, eased through her Dubai Tennis Championships opener on a second day dominated by the seeds.

Rybakina was beaten in last season's Dubai decider by Simona Halep, one of five WTA Tour finals she reached in a breakout year.

The Kazakh, with two career titles to her name, has not played a final since September, however, and entered this week's tournament with a 4-4 record for 2021.

But her fine form in Dubai continued with a straightforward first match, beating Zheng Saisai 6-0 6-4 in 73 minutes.

"I lost a bit of concentration in the second set," number 14 seed Rybakina said. "Also Saisai played well - she decided to risk stepping in on the returns - so overall I think it was not a bad match."

Garbine Muguruza also built on a final defeat, having come up short in Saturday's Qatar Open decider, thrashed by Petra Kvitova.

Including that event, Muguruza has reached the showpiece match at two of the four tournaments she has entered prior to this latest campaign, which began with a 6-3 7-5 win over Irina-Camelia Begu.

Fellow seeds Madison Keys, Marketa Vondrousova and Anett Kontaveit each also raced through in straight sets.

Petra Martic could not join them, however, going down 7-6 (7-2) 6-4 to Kristina Mladenovic.

Meanwhile, Jessica Pegula continued her rich vein of form in a dominant 6-2 6-1 defeat of Yaroslava Shvedova.

The American reached the quarter-finals of the Australian Open and the last four as a qualifier in Qatar, meaning she is now 11-2 since heading to Melbourne.

One-time French Open winner Jelena Ostapenko also triumphed, while former Roland Garros semi-finalist Amanda Anisimova, still just 19, made a victorious 2021 WTA bow.

But three-time grand slam champion Angelique Kerber continues to struggle for momentum, letting a set lead slip to lose to Caroline Garcia.

Danish teenager Clara Tauson landed a first WTA Tour title as the former junior world number one triumphed at the Lyon Open on Sunday.

The 18-year-old beat Swiss opponent Viktorija Golubic 6-4 6-1 in a final contested by two qualifiers, achieving her breakthrough win in an hour and 29 minutes.

Golubic saved five match points but eventually was put away by Tauson, who has spent most of her senior career to date on the second-tier ITF tour.

She caused a major shock at the French Open in September by beating US Open semi-finalist Jennifer Brady in the first round, and Tauson should now become a more familiar presence at the higher level.

The win carries the youngster into the WTA top 100 for the first time, and it completed an impeccable trip to France that saw Tauson win all seven of her matches, including two qualifying rounds, in straight sets.

She said of her performance: "I think I've been really solid; especially after the first set, I've come out good in every single match."

Quoted on the WTA website, Tauson added: "I just kept my game going. It's been a weird week like that, normally I have some fall-outs, but I haven't had any of those this week, so I'm very happy with that."

Tauson shocked Russian top seed Ekaterina Alexandrova in the first round at the start of the week in Lyon, and Alexandrova lost to another teenager on Sunday as the Dubai Tennis Championships began.

The world number 33 was handed a tough draw against American Coco Gauff, who scraped through 7-6 (7-3) 2-6 7-6 (10-8) in a match lasting two hours and 41 minutes.

Gauff served 12 double faults, including seven in the deciding set, but found a way through to the second round.

Svetlana Kuznetsova, Ons Jabeur and Alize Cornet were among the other winners on day one. The top eight seeds, who include Iga Swiatek, Karolina Pliskova, Elina Svitolina and Petra Kvitova, have all received byes to round two of the WTA 1000 event.