Polish qualifier Hubert Hurkacz stunned top seed Kei Nishikori 7-5, 5-7, 6-2 to reach the quarter-finals of the Dubai Duty Free Tennis Championships on Wednesday.
Hurkacz converted six out of seven break points to beat his Japanese opponent in a little over two hours.
The world No 77 faces rising Greek star Stefanos Tsitsipas or Belarusian Egor Gerasimov next.
The victory represented the first time ever Hurkacz has beaten a top 10 player and it will also be his first appearance at a quarter-final at ATP Tour level.
“Well, (Hurkacz) played good, I think,” Nishikori said after the match.
“I didn’t play perfect today, but I think he was playing good serves. Yeah, better than I thought.”
The match lasted two hours and three minutes and the Japanese player bemoaned the conditions, feeling they knocked him off his stride. For Hurkacz, he pointed to his success on serve as the key to the upset.
“Kei is unbelievable player,” Hurkacz said after the match. “I had to serve good. That gave me some opportunities to attack after the serve, also win couple of easy points. Against such a great player, it’s very important to have some free points.
“I was also, I think, returning quite well. I mean, the match was a little up and down. But, yeah, I’m very happy with the win today.”
World No 113 Ricardas Berankis, who stunned eighth seed Daniil Medvedev on Tuesday, continued his fine form with a 6-4, 6-1 victory over American Denis Kudla.
The Lithuanian qualifier will face Gael Monfils or Marcos Baghdatis in the last eight.
Roger Federer, who is searching for a 100th ATP title, will meet Spaniard Fernando Verdasco later on Wednesday.