Argentine Guillermo Canas stunned world number one Roger Federer for the second time in a fortnight to reach the quarter-finals of the Miami Masters.
Federer had lost to Canas at Indian Wells
Canas ended Federer's 41-match winning run earlier this month but the Swiss looked to be heading for revenge when he led 3-1 in the final set.
But Canas lifted his game to force a tie-break, which he won 7-5 to seal a 7-6 (2-7) 2-6 7-6 (7-5) victory.
Rafael Nadal, Andy Roddick and Tommy Robredo all progresssed.
Nadal had little trouble in reaching the last eight, defeating Juan Martin Del Potro 6-0 6-4, while fellow Spaniard Robredo had a real battle with Czech 24th seed Radek Stepanek before coming through 7-6 (7-4) 5-7 7-6 (7-3).
I was really expecting to win, it was one of those matches I shouldn't have lost
Third seed Roddick beat David Ferrer of Spain 7-5 6-3 and will now play British number one Andy Murray for a place in the semi-finals.
Croatia's seventh seed Ivan Ljubicic recorded a 7-6 (7-4) 6-4 victory over Jarkko Nieminen.
Canas beat Federer in Indian Wells two weeks ago and is only the fifth player to record back-to-back wins over the world number one.
"I don't know what it is the key to beat him, I fight for every point and I think for that I beat him," said the 29-year-old.
"I have luck because I played very well the two matches. For me it's like a dream. To beat the world number one two weeks in a row is amazing."
Federer, who lost only two hard-court matches last season, was disappointed with the defeat.
"I was really expecting to win, it was one of those matches I shouldn't have lost," said Federer.
"But he's a great competitor. He played well both times and I just couldn't put him away.
"He dug deep and played well, I was just not very happy with the way things went. I could have won but I didn't do it."