Roger Federer and Stan Wawrinka exited the Internazionali d'Italia with third-round defeats, while Novak Djokovic and Rafael Nadal overcame setbacks to set up a quarter-final encounter.
Federer admitted he almost withdrew from the second successive tournament due to back problems after defeating Alexander Zverev in the second round, and the issue was still troubling him as he suffered a straight-sets defeat to Dominic Thiem. The 17-time grand slam winner is now a doubt for the French Open.
Wawrinka is the reigning champion at Roland Garros, but he suffered another blow in his preparation for the defence of his title as he let a one-set lead slip to Juan Monaco, ranked 110 places below him.
Nadal and Djokovic showed great determination to overcome first-set losses to advance to the last eight, where they will meet for the 49th time.
Second seed Andy Murray's path into the quarter-finals was far more routine, as he comfortably dispatched Jeremy Chardy 6-0 6-4.
Meanwhile, there were wins for Kei Nishikori and Lucas Pouille.
FEDERER HINDERED BUT THIEM SHINES
The Swiss was evidently not at 100 per cent as he took on Thiem in the third round, but the world number 15 produced a high-quality display to secure a 7-6 (7-2) 6-4 triumph.
Thiem won 47 of 63 points on his serve as Federer, recently back from knee surgery, struggled to find consistency on his return.
The Austrian produced two breaks at 3-2 in the first-set tie-break to move ahead, and the world number two was unable to mount a recovery. He now faces a race against time to be fit for the French Open later this month.
WAWRINKA STUNNED BY MONACO
It has not been the greatest of clay-court seasons for Wawrinka, who is struggling for form ahead of his French Open defence.
After disappointing at the Monte Carlo Masters and Madrid Open, the Swiss admitted he performed within himself against world number 114 Monaco.
"It was not a great level today. I was trying to fight, trying to find a solution, but in the end I didn't find a good balance between playing some long rallies and being aggressive. He just played a bit better, and I didn't take my chances," Wawrinka said.
DJOKOVIC AND NADAL POWER THROUGH
Thomaz Bellucci made a phenomenal start to his third-round meeting with defending champion Djokovic, taking the first set to love despite hitting just two winners. The Serbian showed the strength of character befitting a world number one in pursuit of a 30th ATP 1000 title, fighting back to win 0-6 6-3 6-2.
Nadal had shown a similarly strong mentality earlier in the day. The Spaniard put in a display of grit and determination after losing a first-set tie-break to Nick Kyrgios, taking the match 6-7 (3-7) 6-2 6-4.
Kyrgios received treatment during the second set and his body language soon showed he felt the game slipping away from him.
TWO BAGELS FOR GOFFIN
A red-hot display from David Goffin saw him account for Tomas Berdych in just 50 minutes, storming to a brilliant 6-0 6-0 win.
The Belgian staved off three break points in the fourth game of the second set before serving out the match to become the first player to double-bagel a top-10 opponent since Roger Federer overcame Gaston Gaudio at the ATP World Tour Finals in 2005.