Alexander Zverev cruised into the US Open semi-finals with a straight-sets win against South Africa's Lloyd Harris.

Fourth seed Zverev was untroubled after clinching a tight first-set tie-break and edged closer to a second successive final appearance at Flushing Meadows by defeating Harris 7-6 (6) 6-3 6-4 in two hours and eight minutes.

Harris, playing in his first Grand Slam quarter-final, went toe to toe with Zverev in the first set, breaking the German's serve to take a 5-3 lead and then serving to go one set up.

But Zverev broke straight back and, after both players had held serve to force a tie-break, he kept his nerve as the tension mounted to win 8-6, despite two mini-breaks against him.

Zverev pounced again on Harris' serve to open up a 3-0 lead in the second set and sealed it 6-3 with his first set point after 36 minutes.

Harris was broken in both his next service games to trail 4-0 in the third set and appeared to lose heart as Zverev closed in on victory.

World number 46 Harris then rallied to extend the match. He broke Zverev for the second time to trail 4-2 and hauled himself back to 5-4, but it was a brief recovery.

Zverev, who let slip a two-set lead to lose to Dominic Thiem in last year's final, avoided further scares, sealing victory on serve with his first match point.