US Open semi-finalist Frances Tiafoe aimed a torrent of expletives at the chair umpire after losing his third-round match at the Shanghai Masters on Tuesday.

Tiafoe targeted umpire Jimmy Pinoargote in a minute-long tirade after his 5-7, 7-5, 7-6 loss against unseeded Roman Safiullin. The American was angered after being docked his first serve for a time violation at 5-5 in the decisive tiebreaker.

Pinoargote judged that Tiafoe was not making a genuine attempt to serve when he tossed the ball in the air at the baseline. Tiafoe at first protested before continuing with the match. “No, no, I tossed the ball up … I was ready to serve,” Tiafoe said to Pinoargote. “Dude, that’s the rule.”

Two points later, the match was over and he congratulated Safiullin at the net before turning toward the umpire’s chair. “Fuck you, man! Fuck you! Seriously, man. You fucked me out of the fucking match,” Tiafoe said to Pinoargote. Before leaving the court, Tiafoe added: “Never again.”

Tiafoe could face fines for verbal abuse of an official and for using obscenities. The tournament can take away some of his prize money, and the case could also be sent to the ATP Member Fines Committee for further investigation. The ATP rule book calls for fines of $60,000 at Masters 1000 tournaments. A tour spokesman said no decision has yet been made on the matter.

Safiullin advanced to face Novak Djokovic in the round of 16.

Tiafoe had a stellar run of form in the summer reaching the final of the Cincinnati Open, where he lost to Jannick Sinner, then reaching the semi-finals at the US Open where he lost in five sets to fellow American Taylor Fritz.