World No 2 Zverev took the first set 7-6(7/5) after more than an hour of battle with Alcaraz and confirmed his place in the semifinals regardless of how the match finishes.

Alcaraz, who won at Wimbledon and Roland Garros this season but has struggled for form in Turin, has his destiny out of his hands.

If the Spaniard beats Zverev he can still be eliminated if Casper Ruud beats Andrey Rublev in straight sets.

A defeat would mean Alcaraz has to hope for an unlikely straight-sets victory for Rublev, who has lost his last six Finals matches, to have any chance of getting through.

Zverev’s qualification from the John Newcombe Group means that three of the four semifinal spots have been filled, with Jannik Sinner and Taylor Fritz through from the Ilie Nastase Group.