Karlovic was serving for the match while leading 5-4 in the second set but Monfils broke and prevailed in the tie-break.
The break was the first time Karlovic failed to hold serve on 54 occasions in the tournament.
“I was serving for the match. If it was normal match, I would win it right there,” Karlovic said. “My service stopped at that moment. It happens, I guess. I’m not used to that. But it happens.
“I was going to win, and then I lost my serve. That is tennis.”
Monfils added another service break early in the third set to take the momentum and pushed on for the win.
(Writing by Jahmal Corner in Los Angeles- Editing by Peter Rutherford)
