Bernard Tomic, returns a shot from Gilles Muller during their US Open first round match. Photo: AP Photo/Michael Noble

NEW YORK - Volatile Australian Bernard Tomic admitted on Monday that he's "not the smartest" guy in the world but insisted he has no regrets over his frequent controversial outbursts.

Tomic's first match since his first-round loss at Wimbledon - and his subsequent complaints that he was "bored" with tennis and a sport that has brought him over $5 million in prize money was just a "job" - ended in predictable defeat.

He went down 3-6, 6-3, 6-4, 6-4 to Luxembourg 19th seed Gilles Muller in the US Open first round after missing the entire summer hardcourt season with illness.

But despite his outburts after Wimbledon, which also saw him dropped by racquet manufacturer Head, Tomic says he has no regrets.

"It's not like I can go and start a real estate business or a restaurant. I would have no idea. My job is to play tennis," he said.

"I'm not the smartest person in the world - I'm not going to be able to do a doctor's degree.

"But I was honest with my opinions. Sometimes it's better to be honest rather than hiding it and not telling your thoughts."

Tomic has plenty to think about. His ranking is now 146 from a career high 17.

It's his lowest since he was 158 in 2011 and will sink further after failing to defend points from impressive runs last year in Toronto (fourth round) and Cincinnati (quarter-finals).

"It's been my fault. I need to turn it around and I can do it like when I was 140 and finished the year at 16 or 17," he said.

"I'm only 24. Tennis is my life. If I can win a major or two before I retire, I will be happy."

Tomic has won just nine matches this year and had suffered first round exits at the three of the four Slams.

But he still believes he can return to the top 20 and has time on his side.

"I have the motivation although I considered not coming here and maybe starting again in Asia," Tomic said.

"I will lose a lot of points and that's a concern but my health is the most important thing."

Tomic needed treatment from the trainer during his loss to Muller, who defeated Rafael Nadal on his way to the Wimbledon quarter-finals last month.

"Yeah, I tried to find a way back in to the match and gave it my best shot. There's stuff I need to work on."

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