Sinner holds a 2-1 advantage over Alcaraz with both wins coming this year at Wimbledon and Umag.

"I believed in myself, it was pretty tough," said Alcaraz.

"I was a break down in the fifth set. It was tough to come back after losing the fourth set."

Alcaraz overcame a 0-2 deficit in the first set to seal the opener and was a break ahead early in the second before the 33-year-old Cilic stormed back to level the contest.

Alcaraz pounced in the 10th game of the third set to carve out the only break and a two sets to one lead.

The Spaniard twice had Cilic on the ropes late in the fourth set but allowed four break points to slip away.

Cilic grabbed his unexpected lifeline to take the match to a fifth set decider.

But Alcaraz, having wasted six break points in the fourth set, finally converted for what was a key 3-1 lead.