World number one Jannik Sinner was forced to retire from the Cincinnati Open final against Carlos Alcaraz due to illness, just days before beginning his US Open title defence.

Sinner looked unwell from the outset, losing the opening five games in just 23 minutes on a sweltering day.

After treatment and a brief discussion with the trainer, the Italian tearfully told officials he could not continue, apologising to fans before embracing Alcaraz at the net.

The Spaniard, ranked world number two, consoled his rival and later admitted he would have preferred to win differently.

“You will come back even stronger like you always do. That’s what true champions do and you are one,” Alcaraz said.

The result hands Alcaraz his first Cincinnati crown and seventh title of the season, but Sinner’s setback raises concerns ahead of Flushing Meadows.

He is scheduled to feature in mixed doubles on Tuesday, though participation now appears in doubt.

Despite the disappointment, Sinner retains his world number one ranking and his hard-court streak of 26 wins remains intact.

The two men are once again expected to be the leading challengers in New York, where they can only meet in the final.