Shanghai, China, 12 October 2016 | AAP

In-form Nick Kyrgios claims he struggled during his routine 6-4 6-4 first-round triumph over Sam Query at the Shanghai Masters.

The 21-year-old, whose victory in the Japan Open on Sunday moved him to a career-high 12th in the world, extended his winning run to six matches in just 53 minutes.

However, when asked why he was unusually quiet on court the mercurial Canberran admitted it was down to fatigue.

“I was feeling very tired. It was just tough … maybe I just wanted to get the job done,” he said.

“I didn’t have the greatest sleep last night and obviously got in late the day before. The ride to the courts isn’t great either.”

Kyrgios next faces Mischa Zverev, the older brother of fellow ATP young gun Alexander.

Meanwhile, injury forced Bernard Tomic to retire midway through his first-round clash with Spain’s Roberto Bautista Agut.

Tomic was trailing 3-0 in the second set having lost the opener 6-3 when he decided he wasn’t fit to continue.