Italy will play the United States in the final of the inaugural United Cup in Sydney after defeating Greece in a semifinal of the mixed teams competition on Saturday. (More Tennis News)

Stefanos Tsitsipas kept Greek hopes alive by defeating Matteo Berrettini 4-6, 7-6 (2), 6-4 in a clash between two Grand Slam finalists after Italy won the first two singles on Friday.

The world No. 4 held his nerve in an enthralling contest before breaking Berrettini for the first time midway through the deciding set to maintain his unbeaten record in the United Cup.

“Somehow I hung in there. He is a big server. He hits some bombs consistently. You have to accept that, move on from that point, and concentrate on your serve,” Tsitsipas said.

But Lucia Bronzetti clinched the finals berth for Italy by beating Valentini Grammatikopoulou 6-2 6-3 to give her nation an unassailable 3-1 lead in the tie played at Ken Rosewall Arena.

“We are a great team and I am so excited, so happy right now,” she said.

All five matches in the final between the United States and Italy will be played in Sydney on Sunday.

Earlier on Saturday, Taylor Fritz beat Poland's Hubert Hurkacz 7-6 (5), 7-6 (5) to clinch the U.S. a spot in the final.

Fritz put the U.S. up 3-0 in the best-of-five matchup, and 2017 U.S. Open runner-up Madison Keys then made it 4-0 by defeating Magda Linette 6-4, 6-2.

Jessica Pegula partnered Fritz to a 6-7 (5), 6-4, 10-6 victory over Alicja Rosolska and Lukasz Kubot to sweep the semifinal for the U.S.

Pegula and Frances Tiafoe had given the Americans a big lead by taking Friday's opening singles matches, including Pegula's straight-set victory over No. 1-ranked Iga Swiatek.

In the second tiebreaker of his match, the ninth-ranked Fritz had success during rallies by targeting the forehand wing of the 10th-ranked Hurkacz, drawing errors on crucial points. Hurkacz was clearly angered after making three forehand mistakes in succession to drop a tiebreaker he had led 5-4.

“No one could really get through for a (service break), but I think the difference in the tiebreakers is that I served well and put some returns in the court, played some really solid points and didn't give him anything,” Fritz said.

Fritz has represented the U.S. in the Davis Cup but said combining with the country's best female players enhanced the experience in the new, 18-nation team competition.

“I have played with Team USA a lot and I think it is a huge advantage this time having the girls in our team because it just makes the whole team so much stronger,” he said.

“I am super excited going into the finals and I think we have been the favorites all week.”