The precocious world number 14 lost 6-3, 6-1 against the young qualifier in a match in which he criticised fans and received a code violation for swearing.

At one stage, he began walking back to his chair before a serve from Zverev had landed, while he also patted the ball over the net on several occasions.

He responded to booing by fans by claiming "I don't owe them anything".

The 21-year-old, who has repeatedly faced accusations of "tanking" in matches in the past, claimed to be "bored" during his first round victory against United States' Sam Querrey yesterday.

He admitted today that he "took the easy way out" and "tapped out a little bit", but criticised the crowd for booing him.

"I feel like if they knew what they were talking about they'd be on the tennis court and being successful," he said.

Kyrgios, who won the Japan Open last week, is considered one of world's most exciting young players, but has faced numerous disciplinary problems in the past.

He was fined last year for a foul-mouthed outburst while playing in Shanghai, while he also received a suspended 28-day ban for making a sexual comment about Stanislav Wawrinka's girlfriend during a match.

It overshadowed a day on which Serbia's Viktor Troiki produced one of the best performances of his year to beat Spaniard Rafael Nadal 6-3, 7-6 for a first win in five attempts in their second round clash.

"I played really well," he said afterwards.

"I was aggressive, I served well, I hit the ball nice."

Britain's world number two Andy Murray eased into the third round with an impressive 6-3, 6-2 victory over US world number 24 Steve Johnson.

Britain's Kyle Edmund was knocked out in the second round, beaten in 6-3, 6-4 by US Open champion Wawrinka.

Canada's Vasek Pospisil set-up a third round meeting with Serbian world number one Novak Djokovic after beating Bulgarian Grigor Dimitrov 7-5, 7-6.