DUBAI: In a stunning upset at the Dubai Duty Free Tennis Championships on Thursday, Tallon Griekspoor toppled top-seeded Daniil Medvedev to secure the most significant victory of his career and leave the defeated world No. 6 smashing his racquet in frustration.

Showing remarkable resilience, Griekspoor rallied from a set down to claim a dramatic 2-6, 7-6 (7), 7-5 win. The Dutchman saved four match points in the second set before closing out the match at the fourth opportunity to earn a place in the ATP 500 semifinals, where he will face No. 4 seed Stefanos Tsitsipas.

Griekspoor’s path to the final four has been anything but easy. In the opening round, he survived three match points against qualifier Roman Safiullin, and in the second he took down defending champion Ugo Humbert of France.

Now, with Friday representing his eighth ATP Tour semifinal, the 28-year-old Griekspoor continues to prove his mettle against the sport’s elite. “I’m absolutely thrilled with this win,” he said.

“I had to fight off a few match points in the second set … Daniil is an incredible player and competitor. He’s been at the top of the game for years, so this is a huge victory for me.”

In a one-sided first set, Medvedev was quick to anticipate Griekspoor’s aggressive forays to the net, countering with precision and wrapping up the opening inside just 27 minutes. The Russian played near-flawless tennis, committing just one unforced error in open play and winning every point behind his first serve.

Yet Griekspoor refused to be discouraged. After surrendering an early break, the world No. 47 found his rhythm in the second set, sticking to his serve-and-volley strategy. Facing two match points at both 4-5 and 5-6 on his own serve, he forced a dramatic tiebreak that he ultimately won.

Buoyed by his resurgence — and later admitting to wondering how he was still in the tournament — Griekspoor carried his momentum into the decisive set, waiting patiently before seizing his opportunity in Medvedev’s final service game.

“(Daniil) played unbelievably well in the first set,” said Griekspoor. “I wasn’t doing too much wrong, but he was just better. I just tried to hang in there, even after going a break down in the second.

“Once I broke back, I felt the momentum shift a little in my favor. I had some luck on the match points I saved and in the second-set tiebreak, and even when I had match points myself, it took a few tries to close it out.”

Medvedev, who had been seeking a third successive Dubai semifinal, was asked what changed in the second set, responding: “(Tallon) started playing better in some moments. I do think in a way he got lucky with some shots, but that’s tennis.

“When I say lucky, he also went for it, so he deserves it. It’s on his side this week, luck. Sometimes it happens: you go all the way like this — a little bit crazy. Let’s see where it brings him.”

For now, it has brought him to the semifinal in Dubai and a tie with former world No. 3 Tsitsipas, after the Greece star outlasted Italy’s Matteo Berrettini to win 7-6(5), 1-6, 6-4, in a match that went on until after midnight.

The victory ensured a first semifinal appearance since July for Tsitsipas, a two-time Grand Slam finalist. “It’s a great feeling being back so deep in a tournament,” he said.

“It brings a smile to my face to know I’ve been playing good tennis to get to the semis of one of the biggest 500s. It was a difficult match, lots of ups and downs.

“My first set was a great effort to finish it off, but I didn’t really deliver in the second — it was pretty poor. I find it actually quite confusing how I managed to win in the end because it felt like I was going through some mental battle during the match.”

In the other half of the draw, the in-form Felix Auger-Aliassime defeated Croat Marin Cilic 6-4, 3-6, 6-2 to book a second semifinal appearance in the space of a week. The Canadian fought for 2 hours, 18 minutes before Cilic, facing match point on serve, sent a forehand wide.

The former world No. 6 fired a total of 13 aces and broke the Croat three times to reach his fourth semifinal of 2025. “It’s been a great start,” said Auger-Aliassime of his Tour-leading 15 wins this season.

“Of course there’s the work, but then there’s also just seizing opportunities. Sometimes you have to be fortunate.”

He added: “This week, I won three three-set matches that went back and forth. Now the level is so high everywhere, the margins are really small, but I’m glad that it went my way and another semifinal, it’s great.”

The Canadian will face Quentin Halys on Friday after the French qualifier reached his first ATP 500 semifinal by fighting back from a set down to beat Lucky Loser Luca Nardi 2-6, 6-3, 7-6(5). Halys had earlier this week stunned third seed Andrey Rublev, who won in Dubai in 2022.

“The end was crazy,” Halys said. “We were missing some easy shots and playing some crazy rallies … I’m super happy about the win and how I handled the end of the match.

“I’m coming from the qualifiers; I didn’t have many matches before this tournament. The way I’m playing this week is crazy good.”