Novak Djokovic dug deep in the face of fierce Roman resistance to set up a showdown with Rafael Nadal in the men's final at the Internazionali d'Italia.

World number one Djokovic came from a set down overnight to beat Stefanos Tsitsipas 4-6 7-5 7-5 early on Saturday, before returning to the court to face Italian Lorenzo Sonego in the evening.

The Rome crowd raucously rallied behind Sonego, who beat Andrey Rublev earlier in the day, and the 26-year-old rose to the challenge but eventually fell to a 6-3 6-7 (5-7) 6-2 defeat.

Djokovic had match points before serving for it at 6-5 in the second set, yet it was to prove a stirring game as the noisy home crowd encouraged Sonego, who snatched a gutsy break. The tie-break looked set to be wholly one-sided when Djokovic raced 3-0 ahead, but it was soon back on serve, partisan spectators at the Foro Italico roaring in delight at a double fault from the Serbian.

From 4-2 behind, Sonego surged to 6-4 ahead in the tie-break. He failed to convert a first set point when ripping a forehand into the net, but the set was his when Djokovic sent a backhand service return long.

Sonego then had 0-40 against the Djokovic serve at the start of the decider, but he could not force the break, and the top seed gained strength from that escape, eventually cruising to victory.

Five-time Rome champion Djokovic said on Amazon Prime: "I bounced back very well after the second set. Maybe if he started with a break up in the third, things would look differently. I also had my chances and I only had myself to blame for not closing the match in straight sets.

"But he's a quality player, very dynamic, it's not easy to play against him and obviously he had the crowd behind him. It was an electric atmosphere. In the end I managed to close out the match really well."

Looking ahead to tackling Nadal, Djokovic said: "I need to recover. Hopefully I'll have fresh legs because that's what I definitely will need and it's necessary to have a chance against Rafa. He also had some tough matches [this week] and hopefully I'll be fresh and I'll give it all."

While Djokovic and Sonego thrashed away into the night, nine-time champion Nadal had no such workload issues on Saturday.

Nadal beat Alexander Zverev on Friday to set up a semi-final against American Reilly Opelka, and the Spaniard snatched a 6-4 6-4 win from that contest to reach the title match.

Novak Djokovic's Internazionali BNL d'Italia quarter-final with Stefanos Tsitsipas was halted by persistent rain on Friday with the world number one a set and a game down.

Reigning champion Djokovic, who is seeking a sixth triumph in Rome, struggled to get going against Tsitsipas and trails 6-4 2-1 ahead of the scheduled resumption of play on Saturday.

The top seed lost serve in the first game and continued to make some uncharacteristic errors that saw him trail 4-1 at one point.

While Djokovic did earn a first break in the sixth game, Tsitsipas stood firm to take the opening set and was in total control when again breaking his opponent early in the next set.

However, soon after the Greek had opened up a 2-1 advantage, the worsening conditions led to a pause in proceedings and organisers were eventually forced to bring the day's play to an end.

Djokovic, who converted just one of his six break point opportunities, will return to the court on Saturday and will need to improve if he is to join Rafael Nadal in the final four.

Nadal exacted some revenge on Alexander Zverev earlier on Friday to reach the semi-finals for a 12th time.

The Spaniard lost to Zverev at the same stage of the Madrid Open seven days ago but responded to questions over his form by easing through this latest encounter.

Nadal, who saved two match points before beating Denis Shapovalov on Thursday, raced 4-0 ahead in the first set against Zverev and had little trouble seeing the job through.

Aiming for a record-extending 10th title in the Italian capital, Nadal saved all eight break points he faced in the second set to advance 6-3 6-4 in two hours.

"I played more solid than Madrid. Conditions are different," he said in his post-match interview. "Here the conditions are a little more normal. I was able to control a little bit more."

"I'm happy. I played a very solid match with not many mistakes, playing the way that I have to. It's an important victory for me against a great player."

Nadal will face Reilly Opelka for a place in the final, the American beating qualifier Federico Delbonis 7-5 7-6 (7-2) to reach his first ATP Masters 1000 semi-final.

Opelka entered the tournament on a six-game losing streak, but he kept his good run going in Rome by earning the only break of the opening set in the 12th game.

Both players held throughout the second set and it was big-serving Opelka who prevailed 7-2 in the tie-break.

The day's other quarter-final between Lorenzo Sonego and Andrey Rublev also fell victim to the bad weather and will get under way on Saturday.