Fourth seed and tournament favourite Andrey Rublev has beaten former champion Philipp Kohlschreiber 7-6 (7-4) 6-2 to power into the semi-finals of the Halle grass court event.

Russia's Rublev rallied from 4-2 in the tiebreak with five unanswered points and never looked back back on Friday after breaking in the opening game of the second for victory in one hour 21 minutes over 2011 winner Kohlschreiber.

"I am happy with my performance to reach the semi-finals for the first time," said Rublev, who hit 29 winners.

"The first set was really tough. He was up in the tiebreak and I came back, which was the key.

"After the first set, I think he mentally went down and I was pumped up. I hit a couple of good returns in the first game of the second set."

Rublev is the highest seed left as No.1 Daniil Medvedev was ousted along with third seed Alexander Zverev, while second seed Stefanos Tsitsipas withdrew before the start after his gruelling French Open final and the death of his grandmother.

Rublev next plays Georgian qualifier Nikoloz Basilashvili, who beat Lloyd Harris of South Africa 6-4 7-6 (7-5).

Canada's Felix Auger-Aliassime, a Stuttgart runner-up last week on the surface and fresh from eliminating Roger Federer in the previous round, also reached the last four 6-3 6-2 over American qualifier Marcos Giron.

"I've been playing well these past two weeks, believing in myself a lot and dominating my service games," said Auger-Aliassime, who fired 25 winners.

He will meet France's Ugo Humbert who saved seven of eight break points as he outlasted American Sebastian Korda 6-2 6-7 (5-7) 6-4 in the last quarter-final match.