Top seed Rafael Nadal overcame fellow Spaniard Fernando Verdasco 6-3, 6-3 at the Rome Masters on Friday while Roger Federer beat German qualifier Mischa Zverev 7-6, 6-2 to book a semi-final with holder Novak Djokovic.
Serb Djokovic eased through with a 6-3, 6-4 triumph over Argentine fifth seed Juan Martin Del Potro.
Nadal next faces Chilean 12th seed Fernando Gonzalez, a 2-6, 6-3, 6-4 winner over Argentine qualifier Juan Monaco.
Sixth seed Verdasco, who pushed Nadal hard in a five-setter at this year's Australian Open, was on level terms after an exchange of breaks in the first two games.
The world number one over-hit a number of shots but could not be budged off his serve again, pulling off a couple of sublime lobs as he found his rhythm to take the first set.
It was tight in the second set too until the eighth game when Nadal broke again after Verdasco hit an easy backhand volley wide at the net.
"I didn't play my best," Nadal told a news conference after he had saved five break points in the second set.
"I made some mistakes especially in the second set. I was a little bit lucky (because) he made mistakes on some important points."
Zverev, 21, gave Federer a good fight in the opening set.
The German served superbly, attacked the net well and showed character to save two break and set points in the 10th game, which was interrupted for a few minutes when a spectator was taken ill.
Zverev was unable to trouble the second seed on his serve, however, and Federer eventually took the set 7-3 on a tiebreak with a splendid cross-court forehand pass.
Federer cruised home in the second although Zverev had the satisfaction of saving two match points before going out.
"That was a good test," said the Swiss. "I had to come up with some passing shots. It's always good when you're on the back foot and you have to come up with some good shots at the right time.
"Seems like he's a talented player. I think he's got potential and he showed it this week."
FINE RETURNS
Djokovic produced some fine returns to take Del Potro's big serve in the fourth game after an early trade of breaks and went on to seal the first set with an ace.
Del Potro had Djokovic under pressure on his serve at the start of the second but, after failing to convert two break points in the fourth game, he dropped his head and the third seed ruthlessly capitalised to get another breakthrough.
The Argentine saved three match points before firing into the net to let Djokovic through.
"Physically I think I'm stronger (than last year) and I'm combining patience with aggressiveness in certain moments," Djokovic said.
"It's really important on clay to be confident in yourself, that you can play a lot of long rallies, be patient and have big weapons to finish off the points. That's what I did.
"I look forward to (meeting Federer). It's a challenge for both of us.
"I think we've played each other only twice on clay and he won both times in Monte Carlo. I think I have a good chance."
