Monte Carlo - Rafael Nadal has fought off a challenge from John Isner to earn a 7-6 (8/6), 4-6, 6-3 win that took him into the quarter-finals on a day of upsets at the Monte Carlo Masters on Thursday.
Nadal, bidding for a ninth title on the clay of the Country Club, was tested by a dozen aces from Isner, a huge hitter not noted for his finesse on the dirt.
But the American 15th seed put up a massive effort to stay level almost throughout against Spain's king of clay, who is still searching for consistency and confidence in this tepid season.
Nadal won the title every year from 2005 to 2012 and has lost just three times in 55 matches at the tournament.
Earlier, Roger Federer joined holder Stan Wawrinka as an upset victim as the 2014 finalist lost 6-4, 7-6 (7/5) to France's Gael Monfils.
Before that, Grigor Dimitrov had stunned seventh seed Wawrinka 6-1, 6-2 in the third round.
The exit of 2014 Australian Open champion Wawrinka came a year after he won his first and only Masters 1000 title here.
Wawrinka was well off his game, out in 54 minutes with 41 unforced errors and just four winners against ninth seed Dimitrov. And he is now in danger of losing his top-10 ranking place.
World number two Federer missed the chance to reach the last eight in the principality, weighed down by 38 unforced errors against Monfils.
After losing a break for 3-1 in the opening set and standing 5-3 in the second-set tiebreak, 17-time Grand Slam winner Federer could not make much progress against the flashy French opponent who beat him in a Davis Cup rubber last November.
But the Swiss is far from giving up hope only a few days into the spring clay campaign leading to the Roland Garros start on May 24.
"This is not going to put me under too much. It's the first tournament on clay. I was really hoping to do better because I felt there was an opportunity.
"Unfortunately, Gal played well today. It was always going to be a tough match.
"It was a good week for me anyway to come here and practice with the best, play a couple of matches. At least it gives me some information, if I'm trying to be a bit positive right now.
"I'm going to go back to Switzerland and practice really hard, you know, from whatever the plan's going to be from tonight on until Istanbul.
"This is good time I should utilise in the right way. I'm looking forward to that.
"I'm playing Istanbul, Madrid. We'll see what happens with Rome. It was never sure I was going to play that anyway."
Fourth seed Milos Raonic beat Spain's Tommy Robredo 6-3, 3-6, 6-3 while sixth seed Tomas Berdych defeated Roberto Bautista Agut 7-6 (9/7), 6-4.
US Open champion Marin Cilic, the number eight, defeated French 11th seed Jo-Wilfried Tsonga in a match of players returning from injury 6-3, 7-6 (7/5).
Results on the fifth day of the Monte Carlo Masters on Thursday (x denotes seeded player):
David Ferrer (ESP) bt Gilles Simon (FRA) 6-2, 6-7 (3/7), 6-1
Novak Djokovic (SRB x1) bt Andreas Haider-Maurer (AUT) 6-4, 6-0
Grigor Dimitrov (BUL x9) bt Stanislas Wawrinka (SUI x7) 6-1, 6-2
Milos Raonic (CAN x4) bt Tommy Robredo (ESP x16) 6-3, 3-6, 6-3
Gael Monfils (FRA x14) bt Roger Federer (SUI x2) 6-4, 7-6 (7/5)
Marin Cilic (CRO x8) bt Jo-Wilfried Tsonga (FRA x11) 6-3, 7-6 (7/5)
Rafael Nadal (ESP x3) bt John Isner (USA x15) 7-6 (8/6), 4-6, 6-3
Tomas Berdych (CZE x6) bt Roberto Bautista (ESP x12) 7-6 (9/7), 6-4