Injured Lloyd Harris downed by Alexander Zverev in Cologne quarter-finals

Auger-Aliassime won 19 of 22 service points in the third set to retire from Bautista Agut, and he broke at his only breakpoint of the set.

"I struggled on the opening game on my serve, and since then everything went uphill", Auger-Aliassime said. "As a player you know you're happy when your shots are going where you want them to go, and that's really how I felt today".

Top seed Alexander Zverev has continued his hunt for a first title of 2020 by advancing to the Cologne Indoors semi-finals with a hard-fought 6-4 3-6 6-0 victory over South Africa's Lloyd Harris.

The second-seeded Roberto Bautista Agut will meet Canada's Felix Auger-Aliassime in the other semifinal.

Auger-Aliassime will hope the close the deal in another way on Sunday.

"I have got to do a better job of keeping my focus until the end of a match".

"This is our first final, but probably not the last", said the 21-year-old Canadian after he defeated the Spaniard, 6-3, 1-6, 6-3, to reach his third final of the year.

Zverev is through to his third semi-final of the year where he will face Alejandro Davidovich Fokina.

- With files from The Associated Press.