On a day when Aussie No.1 Alex de Minaur was also comfortably tamed by Canadian Felix Auger-Aliassime on Wednesday, Kyrgios's 6-3 6-2 capitulation in just 50 minutes to the big-serving American looked concerning with the season's final grand slam less than a fortnight away.

Needing treatment on a troublesome left knee, it looked as if all the Aussie's breakthrough matches over the past month may have begun to catch up with him as he ended up not even able to rouse himself into any state of high dudgeon after some early rows with the chair umpire.

Some of the crowd in Cincinnati clearly weren't too impressed either with the amount of effort they'd seen from the mercurial Canberra figure as there were a smattering of boos at the end of the one-sided affair.

"He doesn't look strong enough to do it week in, week out," former US Open finalist Greg Rusedski noted on Amazon Prime.

"You can hear the boos around the stadium. They didn't feel like he'd given his best effort out there. But I think you've got to give him some slack ... he's given it a go."

Kyrgios, who'd been on a roll with 16 wins in his previous 18 matches stretching back to the start of his famous Wimbledon run, looked to be distracted from the start, muttering about it "being only a matter of time before it all unravels".

He started with a running argument with umpire Renaud Lichtenstein about his failure to control spectators moving about during points, telling the official: "Why don't you do your job properly?"

Kyrgios was also told three times by Lichtenstein not to keep swearing, although the Aussie got away with not receiving an official code violation.

In his first meeting with Fritz, he was broken in a careless sixth game, as he clearly started to feel problems with his knee.

Facing a gambler playing at double speed and serving up all-or-nothing double faults, Fritz remained calm amid Kyrgios's chaotic work, even latching on to his underarm serve to send a winner flashing past the Australian.

Earlier, de Minaur has been handed a similarly brutal lesson, the Australian No.1 being swept aside, also by a 6-3 6-2 scoreline.

Just as Kyrgios had too much firepower for him the previous week in Montreal, the Sydneysider, who so often finds the very best in the business a step too far for him, was bullied by the young Canadian.

It was a dispiriting experience for world No.20 de Minaur, who, as ever, was not found wanting in effort as he tried to launch a fight back from 4-0 down in the second set.

Auger-Aliassime decorated his emphatic win with 22 winners. The 22-year-old's power earned him four breaks while de Minaur broke just the once when all was nearly lost at 4-1 down in the second stanza, a brilliant effort capped by a rocketing forehand.

But his resistance didn't last long as Auger-Aliassime quickly restored his supremacy, breaking for a 5-2 lead before wrapping up proceedings on his own delivery in just 78 minutes.

Australian Associated Press