Defending champion Alex de Minaur has advanced to the final of the ATP 500 tournament in Acapulco after his British opponent Jack Draper retired in the third set of their last-four clash.

The third-seeded Australian won the first set 6-3, dropped the second 6-2 and was leading 4-0 in the third when Draper, who was visibly diminished physically, called it quits.

World number nine de Minaur will face Casper Ruud in the final.

"I'm happy to be in the final, but I'm hoping that Jack is doing fine," de Minaur said.

"He has a tremendous talent and hopefully he can recover for the upcoming tournaments.

"It's hard to play when your opponent is not OK physically, but you need to remain focused."

De Minaur won his ninth straight match in Mexico as he became the first defending champion to reach the Acapulco final since Spain's David Ferrer in 2013.

Sixth-seeded Ruud defeated second seed Holger Rune 3-6, 6-3, 6-4 in the second semifinal.

AAP