Tomic can't keep his mouth shut

Fiery Australian star Bernard Tomic was at the center of a foul-mouthed US Open controversy on Tuesday when he became embroiled in a lewd exchange with a heckler.

The 23-year-old slumped to a 6-4, 6-3, 4-6, 7-6 (7/0) loss to Damir Dzumhur of Bosnia on the old Grandstand court.

But before he lost the first round match, he also spectacularly lost his composure, angrily barking back at a spectator he accused of deliberately trying to get under his skin.

Courtside microphones picked up Tomic telling the fan: "I will put my **** in your mouth," followed moments later by "I will give you some money to make you feel good".

Tomic apologized for the incident, suggesting his Croatian roots may have been a factor in the clash against his Bosnian opponent.

"I apologized for what I said. I think when the guy left after the first set, the crowd got happy because he was a bit annoying," said Tomic, who was unable to recall what was said to him.

"He was just sort of saying negative stuff. I didn't know who it was because I was just focusing on the court.

"It was tough to figure out in the background. It's passed and I don't really care who this guy is. He definitely baited me.

"I had problems on the other end, as well, with a few people in the corner. They were saying some negative stuff to me, in my language of Serbian-Croatian. The microphones didn't pick that up. But I obviously caught the blame for that."

Tuesday's controversy was the latest to hit Tomic.

At Wimbledon, he was forced to apologize for using the word "retard" during a media conference.

That outburst came after he had been widely condemned for his boorish behavior in Madrid when he turned his racket the wrong way to face a match point against Fabio Fognini.

Tomic later told reporters: "I don't care about that match point. Would you care if you were 23 and worth over $10 million?"

In July last year, he was arrested in Miami after a wild party in a hotel penthouse suite.

He was then dropped from the Australian Davis Cup team and subsequently opted out of the Rio Olympics.

Tomic, seeded 17 for the tournament, committed 78 unforced errors in his tame defeat to Dzumhur, who will face either Illya Marchenko of Ukraine or Croatia's Ivan Dodig.

Dzhumur, who lost to Tomic in New York at the same stage last year, said he didn't hear what was said to the Australian.

"Everyone has their own fans and some can go over the limit," said the Bosnian.

"I have had these kind of problems in the past. But if you listen to the fans too much, it's not good for you."