Nick Kyrgios said he was "bored" as he extended his unbeaten run to six matches with victory over Sam Querrey at the Shanghai Masters.
The Australian, 21, beat world number 29 Querrey 6-4 6-4 in 53 minutes to progress to the second round.
Kyrgios, ranked a career-high 14th in the world, won the Japan Open on Sunday and is closing in on the top 10.
"I was just a bit bored at times," said Kyrgios, when asked why he was not his usual vocal self against Querrey.
"I was feeling very tired. It was just tough. I'm just tired so maybe I just wanted to get the job done."
Kyrgios said his success in Japan, and the travelling involved in playing at the Qi Zhong Stadium, an hour from Shanghai city centre, had taken its toll.
"I didn't have the greatest sleep last night and obviously got in late the day before," he said. "The ride to the courts isn't great either."
It was at the Shanghai Masters last year that Kyrgios was fined $1,500 (£984) for a foul-mouthed outburst, describing the tournament a "circus".