Ivo Karlovic upset Novak Djokovic 6-7(2), 7-6(6), 6-4 at the Qatar ExxonMobil Open in two hours and 16 minutes.
Karlovic fired 21 aces and 49 winners to advance to the Doha semi-finals.
"It was unbelievable," said Karlovic. "When I arrived here, I didn't expect that one. He wasn't able to show his full range because it was windy. I just focused on my game and in the end I was a little luckier."
Karlovic will next face David Ferrer, who beat Dustin Brown of Germany 6-2, 6-2, for a berth in the final.
