British number one Dan Evans produced a superb fightback to beat third seed Karen Khachanov 3-6 7-6 (9-7) 6-4 and reach the European Open semi-finals.
Evans, 30, faced match point in the second set but went on to take the tie-break after a hotly disputed line call.
Early in the deciding set he broke Russian world number 17 Khachanov, before completing victory in two hours 40 minutes.
Evans will face France's Ugo Humbert in the last four in Antwerp on Saturday.
On Saturday, Khachanov said he spoke to the umpire Adel Nour after the match and claimed the official apologised for "the mistakes he made".
The Russian said he apologised to the umpire for his own "rude behaviour".
Having been a set and a break of serve up, Khachanov was outraged when an Evans forehand was not called out, which gave the Briton set point in a tense tie-break.
With no Hawk-Eye technology, Khachanov was reliant on umpire Nour to overrule the line judge and was incensed when that did not happen.
He stormed over to the umpire's chair and said: "It's a joke, it's a joke. Everyone can see it was out.
"What are you doing here? What are you doing here? You don't need to be here."
World number 35 Evans took the second set on the next point as Khachanov kicked the net and then hit the umpire's chair with his racket, earning a code violation.
"At the end of the day, we are all human and able to do mistakes," tweeted Khachanov.
"I didn't want to to insult anyone and act like this. I just couldn't control my temper in those crucial moments... which in the end reflected on the result of the match."