American Taylor Fritz celebrated his 24th birthday by beating doubles partner and close friend Tommy Paul 7-6(3), 6-4 in St. Petersburg on Thursday.

“It makes it even tougher – not just another American, one of my closest friends,” Fritz said.

“It’s never easy playing against a really close friend.”

Fritz took a 3-0 lead in the first set before Paul fought back, but a double fault in the tiebreak gave the set to Fritz. The second was less dramatic, with Fritz breaking and holding serve at critical times to take out the match.

Fritz will next face Australian John Millman, who upset fourth-seed Aslan Karatsev 6-3, 6-2.

Karatsev, who won the Kremlin Cup in Moscow last weekend, blew it at 2-2 in the second set, slamming his racket on to the court and receiving a penalty point that Millman took advantage of.