ACAPULCO, Mexico (AFP) — Defending champion Alex de Minaur booked a return to the Acapulco ATP final on Friday as Britain's Jack Draper retired while trailing in the third set of their semi-final.

Australia's De Minaur will battle for the title on Saturday with sixth-seeded Casper Ruud of Norway, who rallied to beat second-seeded Holger Rune of Denmark 3-6, 6-3, 6-4.

Third-seeded De Minaur was up 6-3, 2-6, 4-0 when Draper called it a day due to an undisclosed illness. The Aussie admitted he'd found it hard to maintain his game plan as Draper faded.

"I think those are the types of situations which are the hardest to control as a player, because you're stuck in two minds," De Minaur said. "One mind is, all right, you can see your opponent hurting. So let's just try and put the ball in the court and make him just miss."

"What you really have to do is play the same style of tennis that you were that got you to that stage. So it's extremely hard to focus in those situations, and often these are the matches that can complicate themselves."

Draper, who had dropped just 11 games in three matches to reach the semis, was piling on the pressure when he received treatment from the ATP trainer and tournament doctor late in the second set.

The left-hander was able to level the match, but he was hindered early in the third as De Minaur raced to a 4-0 lead, and Draper called a halt after he was broken a second time.

De Minaur said he wished Draper a "speedy recovery."

"He's a hell of a player, a hell of a talent and I hope it's nothing too serious," said De Minaur, who is coming off a runner-up finish to Australian Open champion Jannik Sinner in Rotterdam.