American John Isner has made the last four of the Heineken Open after overcoming an injury to beat Philipp Kohlschreiber in a high-quality quarter-final.

Neither player was able to break serve during the match but after three tiebreaks, Isner did enough to squeak through 6-7 7-6 7-6.

In each tiebreak it was only one mini-break of serve that was enough to take the set, though Isner possibly deserved the win after creating more opportunities to break serve than the German did.

Isner, the 2010 champion, is set to play Roberto Bautista Agut of Spain in their semi-final, though there will be some doubt about him making the court on Friday as he was clearly struggling with an injury in the third set on Thursday.

Bautista Agut, ranked 73 in the world, earned his semi-final spot after an easy 6-1 6-3 victory over highly rated American prospect Jack Sock.

The Spaniard handled the disruptions of three rain delays much better than the 21-year-old American, keeping his concentration up.

“On days like this you have to stay focused, and play hard when you start again,” Bautista Agut said.

Sock created a big impression in his first two matches in Auckland but was error-ridden on Thursday, though the Spaniard said the pressure he put on was a factor.

“He made a lot of mistakes, because I was returning everything,” Bautista Agut said.

Bautista Agut reached a career-high 48 in the rankings during 2013 and may have got higher but for injury – he retired injured three times in matches during the year.

“It’s not easy to keep the ranking with those injuries, so this year I want to stay healthy.”