NEW YORK (AFP) — Carlos Alcaraz powered into the semifinals of the US Open on Wednesday as rival Daniil Medvedev battled through a brutal heatwave to join the Spaniard in the Last Four.

Defending champion Alcaraz moved to within one win of a potential dream final with Novak Djokovic with an emphatic straight sets victory over German 12th Alexander Zverev.

Zverev had emerged as a dark horse after a marathon five-set win over Italy's sixth seed Jannik Sinner on Monday.

But the German's hopes of extending his stay in New York were obliterated by a devastatingly clinical performance from Alcaraz, who completed a 6-3, 6-2, 6-4 win in two hours and 30 minutes on the Arthur Ashe Stadium court.

The victory leaves the 20-year-old Alcaraz firmly on course for another final showdown with 23-time Grand Slam champion Djokovic after their Wimbledon classic in July.

Djokovic faces unseeded American Ben Shelton in Friday's other semifinal.

"I'm feeling really comfortable playing on this court, playing in New York," said Alcaraz, who will face Russian third seed Medvedev in the semifinals on Friday.

"I'm feeling strong. I think I'm ready for a great battle against Medvedev," added Alcaraz, who has dropped just one set en route to the Last Four.

Medvedev had earlier secured his place in the semi-finals with a 6-4, 6-3, 6-4 victory over compatriot Andrey Rublev in punishing, furnace-like conditions that the Russian said endangered players.

New York has been sweltering in a heatwave this week, with high humidity and temperatures at Flushing Meadows on Wednesday hitting 35 degrees Celsius.

Tournament organizers confirmed that extreme heat measures were in effect for the quarter-final — but Medvedev was clearly unimpressed.

At one point during the third set, the 2021 US Open champion muttered to a nearby television camera "one player is going to die and they're going to see" as he grabbed a towel.