Daniil Medvedev was ousted from the Indian Wells Masters, the US Open champion and top seed stunned by former world number three Grigor Dimitrov in a thrilling comeback.
Dimitrov had been a set and a double break down against the Russian star on Wednesday, before launching a remarkable rally for his first win over a top-two opponent since 2016.
Meanwhile, second seed Stefanos Tsitsipas and third seed Alexander Zverev both won to secure their spots in the last eight.
MEDVEDEV SHOCKED IN THE DESERT
Dimitrov roared back to triumph 4-6 6-4 6-3 over Medvedev, who had won 18 of his past 19 matches on North American soil.
Bulgarian star Dimitrov trailed 4-1 in the second set after dropping the opener before stunning the first-time grand slam champion midweek.
"I just felt something at 1-4 and I calmed myself down and started to take better decisions and started to control the pace of the game, which I really believed helped me," Dimitrov – the 23rd seed – said. "In the end it was just very solid and smart play."
Dimitrov finished the match with 25 winners, while he was also excellent at the net, helping him claim his first quarter-final appearance at an ATP Masters 1000 event this season.
Medvedev sent down 5-1 aces but only managed a 54 per cent first-serve percentage, while he also faced 10 break points across the match. Dimitrov won five games in a row to claim the second set.
"I don't remember myself losing three service games, even four service games ever, I guess, on hard courts," Medvedev said.
"That shows how slow this court is and the conditions, more like clay, I would say, which I don't like, because to lose serve four times is just unacceptable."
Dimitrov will face eighth seed Hubert Hurkacz in the quarter-finals after he got past Australian Open semi-finalist Aslan Karatsev 6-1 6-3.
Medvedev added: "Grigor played [the] second part of the match better than anybody did against me [at the] US Open that I won. Playing this level, I don't see him losing to anybody, but let's see the result."
ZVEREV MAKES STATEMENT WITH MONFILS WIN
Olympic Games gold medallist Zverev bulldozed his way past 14th seed Gael Monfils 6-1-6-3 en route to the last eight.
German star Zverev claimed his 20th win from his last 21 matches, needing just over an hour to dispatch Monfils.
Zverev claimed 19 of 25 points at the net, hitting 19 winners including 11 with his forehand, while converting four of eight break points.
"I felt well on the court today. Gael is someone I haven't beaten before, so I knew had to play my best tennis and I definitely was not far away," Zverev said during his on-court interview.
Zverev will take on American 31st seed Taylor Fritz, who defeated 10th seed Jannik Sinner 6-4 6-3.
TSITSIPAS OUTLASTS DE MINAUR
French Open runner-up Tsitsipas saw off a tough challenge from Australian Alex de Minaur to secure his spot in the quarter-finals 6-7 (3-7) 7-6 (7-3) 6-2.
Tsitsipas fought back from a set down to win against the 22nd seed, triumphing in two hours, 43 minutes.
Greek star Tsitsipas showed grit to outlast the tiring De Minaur and will face 29th seed Nikoloz Basilashvili after he knocked off fellow seed Karen Khachanov 6-4 7-6 (8-6).
"That was incredible the way I just stayed in the match," Tsitsipas said. "I had to go through so many difficulties in order to find a solution and I executed towards the end of the match."
There were further top-10 casualties, with sixth seed Casper Ruud also bowing out 6-3 6-3 to 11th seed Diego Schwartzman, who will meet Cameron Norrie in the quarters.