NICK KYRGIOS admitted he "took the easy way out" following a 6-3 6-1 defeat to qualifier Mischa Zverev at the Shanghai Masters.
Australian Kyrgios, who won the Japan Open title last week, could face punishment after he was booed off the court during a petulant display that included tame serves and walking out of points before they were finished.
"It was just tough" the 21-year-old said. "Obviously I have played a lot of matches in a row. I am physically tired, mentally tired.
"That's why I'm trying to work on being able to be consistent every week. I just took the easy way out tonight and obviously didn't show up at all.
"I wasn't so much frustrated, I just tapped out a little bit, I guess."
Kyrgios was hit with a code violation for swearing in the first set and was then booed by the crowd as he walked off the court after failing to face a return from Zverev following his own tame serve to trail 4-1.
Sitting in his chair, the world No.14 became involved in a heated exchange with umpire Ali Nili, who told Kyrgios to "act professional and play with your best effort the whole time."
In the second set, when facing game point at 1-1, Kyrgios started to walk off before Zverev's serve had landed in his side of the court.
Later, when Zverev served at 5-1, the Australian responded to heckling from the crowd before conceding the match when he chipped up a return which allowed the German to put away match point after 48 minutes on court.
Kyrgios defended his exchange with the crowd, saying: "They don't know what I'm going through, so no, I don't understand it.
"I feel like if they knew what they were talking about they'd be on the tennis court and being successful as well.
"I don't owe them anything. It's my choice. If you don't like it, I didn't ask you to come watch. Just leave.
"If you're so good at giving advice and so good at tennis, why aren't you as good as me? Why aren't you on the tour?
"You want to buy a ticket? Come watch me. You know I'm unpredictable. It's your choice. I don't owe you anything. It doesn't affect how I sleep at night."
Kyrgios could face a battle to make the season-ending ATP World Tour Finals next month, but the Australian claimed he "couldn't care less" whether he qualified for London.
Kyrgios was more apologetic when he later wrote on Twitter: "Not good enough today on many levels, I'm better than that. I can go on about excuses but there are none. Sorry #StillAWorkInProgress".
The Association of Tennis Professionals' rules state that any player failing to put in "best efforts" in a match can be fined up to $10,000 (£8,200) for each violation.
At Wimbledon 2015, Kyrgios suffered a similar on-court meltdown when losing to Frenchman Richard Gasquet.
Elsewhere in Wednesday's early matches, Great Britain's Andy Murray, the No.2 seed, coasted through to the last 16 after a 6-3 6-2 win over American Steve Johnson to continue his momentum from last week's China Open triumph. No.3 seed Stan Wawrinka, meanwhile, saw off Britain's Kyle Edmund 6-3 6-4, while fifth-seeded Canadian Milos Raonic is also through after a 6-2 6-4 win over Italy's Paolo Lorenzi.
Canadian Vasek Pospisil set up a clash with top seed Novak Djokovic in the last 16 as he beat Bulgaria's Grigor Dimitrov 7-5 7-6 (7/2), however Tomas Berdych, seeded No.7, is out following a 7-6 (7/4) 7-6 (7/1) defeat by Marcel Granollers of Spain.
There was a shock at the start of the evening matches, with No.4 seed Rafael Nadal beaten 6-3 7-6 (7/3) by Viktor Troicki of Serbia, ranked No.31 in the world.
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