Lloyd Harris of South Africa stunned top seed Dominic Thiem in straight sets in the second round of the Dubai Tennis Championships on Tuesday.
Thiem, the reigning US Open champion who was given a bye for the first round, lost 3-6 4-6 to his 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 beaten,” 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 now, match in match out, 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.
He 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.