Rome, Italy (SportsNetwork.com) - Reigning champion Novak Djokovic and second-seeded Roger Federer moved into the final four at the Italian Open, a clay-court French Open tune-up.

The world No. 1 stalwart Djokovic won his third three-setter of the week by holding off fifth-seeded U.S. Open runner-up Kei Nishikori of Japan 6-3, 3-6, 6-1 to extend his current winning streak to 20 matches.

"I have to be honest and say I haven't been playing as well in this tournament as I did at Monte Carlo. The level I want to get on is still not there," said Djokovic. "But little by little it's coming together."

The three-time Rome titlist and two-time runner-up beat nine-time finalist Rafael Nadal (7-2) in last year's final. Djokovic and Nadal have combined to win the last 10 titles at this Masters 1000 tournament.

The Australian Open and Wimbledon champion Djokovic already owns three Masters titles this season. His semifinal opponent on Saturday will be gritty seventh- seeded Spaniard David Ferrer.

In 19 career meetings, Djokovic has won 14 times against Ferrer. Although the Spaniard has won three of their five matchups on clay.

Djokovic has won their last two meetings on clay, including a quarterfinal victory in Rome last year.

The former world No. 1 great Federer eased past sixth-seeded Czech slugger Tomas Berdych 6-3, 6-3 on Day 5 in the "Eternal City."

Along with Monte Carlo, Rome is one of only two Masters titles that the 17- time Grand Slam champion Federer has never won.

"From the baseline I was playing very well." Federer said after besting Berdych. "My serve was not quite there from the beginning. I was hitting too many second serves and he was able to take advantage of that and break early. So it was important to pick it up on the serve, which is maybe the easiest thing to do."

The 33-year-old Federer is a three-time runner-up in Rome, including 2006 and 2013 versus his great rival Nadal, whom he could face on Saturday. The fourth- seeded former No. 1 Nadal is currently battling eighth-seeded Swiss and 2008 Rome runner-up Stan Wawrinka in Friday's nightcap at Foro Italico.

Nadal was last week's Madrid Masters runner-up to Andy Murray, who pulled out of the Rome draw on Thursday, citing fatigue.

The 2010 Rome runner-up Ferrer, meanwhile, got past capable Belgian David Goffin 6-2, 4-6, 6-3 in his quarterfinal affair.

The 2015 Rome titlist will claim $708,000.