Top seed Carlos Alcaraz defeated Alexander Zverev in straight sets on Wednesday to cruise into the US Open semi-finals and keep his title defence on track.

The Spaniard will play third seed Daniil Medvedev on Friday for a place in the final after sweeping Zverev aside 6-3, 6-2, 6-4 in another clinical performance.

Alcaraz was not at his spectacular best but dominated at critical moments with Zverev perhaps feeling the effects of a 4hr 41min outing in the last 16 in the tournament's longest match so far.

The world number one converted all four of his break points, while Zverev failed to take any of his five chances.

"I'm feeling really comfortable playing on this court, playing in New York," said Alcaraz, who has dropped just one set en route to the last four.

"I'm feeling strong. I think I'm ready for a great battle against Medvedev."

The 20-year-old Alcaraz is now 24-1 in his last four Grand Slams going back to the start of last year's US Open. His only loss in that time came to Novak Djokovic in the French Open semi-finals.

Zverev sensed an opportunity when he twice brought up break point in the seventh game, but Alcaraz held firm and then rubbed salt in the wound by smashing a volley at the net to dart 5-3 ahead.

A comfortable service game earned Alcaraz the set and he didn't wait long till to hammer home his advantage, whipping a crunching backhand to break for a 2-1 lead in the second set.

The top seed punished a Zverev double fault by breaking once more for 5-2, cemented with a one-two combination of blistering forehands.

Alcaraz snuffed out a break point in the second game of the third set, thwarting Zverev twice more two games later -- continuing the theme of raising his game throughout when it mattered most.

He needed no second invitation when another opening presented itself on Zverev's serve at 4-all, slashing a wicked forehand to close in on victory before serving it out for a spot in the semi-finals.

mw/rcw