WATCH the Cincinnati Open LIVE in Australia on beIN SPORTS | Subscribe here and take advantage of our 7-day FREE TRIAL

It was far from a convincing display from the Spaniard, who is seeded No.2, but Zverev was under so much physical stress that despite clinging on longer than many others might have, he eventually had nothing left to give.

It was the second straight match in which Zverev had shown signs of physical exhaustion, also needing a medical timeout against Ben Shelton in their quarter-final.

The match started with a delay for a medical incident in the stands as the heat was taking its toll on more than just those on court.

A late burst of Alcaraz brilliance essentially decided the first set before Zverev started to show signs of physical decline.

The No.3 see received a medical timeout at 2-1 in the second set, despite reeling off two straight games as Alcaraz suffered some service yips, coughing up four double faults in one game to hane the German an unexpected break.

But Zverev was clearly struggling in spite of that gift, and was barely moving for the rest of the set before it was mercifully ended by a string of Alcaraz winners.

"Happy for the final but feeling bad for Sascha," Alcaraz wrote on the camera lens post-match, after levelling the pair's head-to-head series at 6-6.

At 22 years and three months of age, Alcaraz is the third youngest player to reach nine ATP Masters 1000 finals after Rafael Nadal (20) and Novak Djokovic (21).

The final showdown with Sinner could be another classic battle after high-quality finals between the pair already this season at the Rome Masters, Roland Garros and Wimbledon.

Alcaraz is one of the few players on the ATP Tour to have the wood on the Italian star, having beaten him in both the Rome and Roland Garros finals and holding a 8-5 advantage in their head-to-head.

But Sinner's Wimbledon win was the most recent result between the two, and he will be hoping to replicate that performance on the Cincy hard courts when the pair meets for the final on Tuesday (AEST).