Jack Draper battled back from a set down to defeat defending champion Frances Tiafoe 5-7 6-4 7-6(1) and seal his place in the semi-finals of the Stuttgart Open.
Draper is set to go past Cameron Norrie and become the top-ranked British male player for the first time in his career after his run in Germany.
He will next face world No. 70 Brandon Nakashima, who advanced after Jan-Lennard Struff pulled out with illness.
The rain wreaked havoc in Stuttgart, forcing an hour-long delay after a magnificent first set, but Draper finished with 31 aces on his way to an outstanding win.
Draper and Tiafoe went back and forth in the early stages of a closely-fought opener, but the Brit was broken in the 11th game, handing the American a chance to serve for the first set.
He made no mistake, holding serve to win the set despite only having two break points against the impressive Draper.
The Brit battled back to level the match with a defiant display in the second set, but Tiafoe refused to give in.
The American levelled the third set at 5-5, saving a dramatic match point before sending the game to a decisive tie-break.
However, Draper held his nerve, romping through the tie-break to seal his last-four spot.
“To come through today was amazing and I am really proud of my effort,” said Draper.
“I think that is the most aces I have ever hit in a match, so you guys have made me hit better serves I think.
“I am really happy with the way I played and the way I served, it was a really high-quality match.
“On these grass courts, Frances was serving well himself so to serve the way I did was a really big positive for me.
“It was a very stop-start day, it is difficult to go out after the losing the first set, I felt I had chances to win that set.
“It is not as hard for me as it is for the fans, they’re sitting in the rain and I really appreciate them coming to watch the tennis, it means a lot.”
Draper is set to replace Cameron Norrie as the new British No. 1 next week.
“I am incredibly happy,” Draper said.
“My last three tie-breaks in the third set I have lost them all, so to come through today is amazing and I am really proud of my level. I am really happy with how I served and it was a really high-quality match.”