An injury to his right shoulder forced the 20-year-old to concede to Tiafoe after his first serve of the second set. The Italian lost the opener 6-2.

“He came out playing really well. He had a chance to go for a break early with some great returns – but he maybe paid for them,” Tiafoe said.

“I thought I was playing at a really high level. “Obviously, I could see he was tugging his shoulder a lot and stayed locked in. I don’t want to win this way, especially for my team and myself. I hope Lorenzo feels better.”

Tiafoe’s win, coupled with the victory for Pegula, means the US only need one victory in the evening session to clinch the inaugural United Cup title.

Tiafoe, ranked No 19 in the world, had to fight to win his own opening service game before breaking in the third game and steamrolling his way to a comfortable first set win.

Musetti, however, was struggling as the match wore on, and after attempting to play following treatment at the side of the court, he stepped over the net to concede.

Pegula, meanwhile, notched up a straight sets win over a battling Trevisan, clinching the opening set 6-4 as both players struggled to hold serve.

She then took command in the second set, winning the first five games before ending a late fightback by Trevisan to secure a straight sets win.