Holder Rafael Nadal provided more evidence that he is regaining his old dominance on clay after an injury-hit 2009 by cruising past Romanian Victor Hanescu 6-3, 6-2 at the Rome Masters on Thursday.
British world number five Andy Murray struggled, however, and lost 6-3, 6-4 to Nadal's Spanish compatriot David Ferrer.
Nadal, who romped to his sixth consecutive Monte Carlo Masters title earlier this month, displayed superb movement throughout and got his first break in the fourth game with a sizzling return.
He produced stunning forehand winners on his way to going 4-1 ahead in the second set.
He then fended off Hanescu's valiant attempts to pull back a break, saving five break points in his last two service games, before sealing victory with a smash at the net, with AS Roma captain Francesco Totti applauding in the crowd.
"Since the start of the clay season I've been playing well and that's important," Nadal told a news conference before admitting to relaxing a little towards the end.
"I played with a little less intensity after going 4-1."
In the last eight Nadal will meet Stanislas Wawrinka, who crushed Swede Robin Soderling 6-3, 6-2.
Murray had snapped a run of three defeats with victory over Italy's Andreas Seppi on Tuesday but he looked below his best in the third-round meeting with Ferrer.
He got in fewer than a third of his first serves in the opening set, which 13th seed Ferrer sealed with a sweet drop volley after breaking in the sixth game.
The poor serving infected other parts of Murray's game and he shook himself a few times, apparently baffled by his own ineptitude, before conceding serve again in the seventh game of the second set.
Clay specialist Ferrer served out to beat the Scot on his least favourite surface and set up a quarter-final with Jo-Wilfried Tsonga.
World number two Novak Djokovic progressed too, with a 6-4, 6-4 win over Thomaz Bellucci that was harder than the score suggested.
Djokovic, the 2008 champion, had to come from a break down in each set against the Brazilian, who put up a lively display but at times had trouble keeping his big serve under control.
The Serbian will now meet in-form Spaniard Fernando Verdasco, who thrashed him in the semi-finals of the Monte Carlo Masters two weeks ago.
Verdasco, fresh from his triumph at last week's Barcelona Open, booked his place in the last eight with a 6-4, 7-6 win over his compatriot Guillermo Garcia-Lopez.
"I don't think I'm the favourite at all. I suppose if I play an aggressive game, then I will have a good chance to win," Djokovic told a news conference when asked about the Verdasco match.
"The last time we played I really didn't feel good on the court. I made a lot of unforced errors and didn't really give the real picture of my game."
After turfing out world number one Roger Federer on Tuesday, Latvian Ernests Gulbis won a final-set tiebreak to scramble past Italian wild card Filippo Volandri.