Frustrated Kyrgios remonstrates with chair umpire

A frustrated Nick Kyrgios has remonstrated with the chair umpire during the second set of his loss to Grigor Dimitrov during the Cincinnati Masters final.

Struggling to make an impact against his sharper opponent, Kyrgios turned his attention to the chair umpire, expressing anger with line calls.

"I know everyone makes mistakes, but come on, man," Kygrios told the umpire.

Watch the full exchange in the video at the top of the page.

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The firebrand went down 6-3 7-5 against the Bulgarian, with the Australian unable to maintain the form which saw him beat world No.1 Rafael Nadal in the quarter-finals.

Kyrgios hit 15 aces to six but was weaker on serve throughout, winning only 36 per cent of points on his second-serve in the second-set.

He was forced to twice save break points in the second set at 3-3.

Dimitrov did not lose a set on the way to winning his first ATP Masters tournament, with Kygrios in full praise of his opponent's fitness.

"I was struggling a couple of weeks ago and he got me out on the practice court. We practised for an hour-and-a-half and I was struggling and he was fresh," Kyrgios said.

"You had me mentally today already. I was like, 'I know this guy's fitter than me'."

Kyrgios will next turn his attention to the US Open, beginning August 28 in New York.

A frustrated Nick Kyrgios has lost the Cincinnati Masters final to Grigor Dimitrov in straight-sets.