'Genuine genius': Nick Kyrgios' secret weapon stuns tennis commentators

Nick Kyrgios brought out the underarm serve early in Australia’s quarter-final clash with Great Britain at the ATP Cup.

The controversial Aussie had commentators full of praise when he caught Cameron Norrie by surprise with an underarm serve early in the first set on Thursday.

Norrie could only bunt a soft return back to Kyrgios, who had advanced to the net before putting away an easy volley winner.

‘THAT’S FOR SURE’: Djokovic hits back over bizarre Nick Kyrgios antics

While some are still critical of the controversial tactic, Mark Petchey was loving it in commentary.

“He’s got that down to a particular art-form in terms of the disguise,” Petchey said on Channel Nine.

“It’s genuine genius the way that he does it.”

There were comical scenes late in the match when Norrie tried to counter the underarm serve by running forwards before Kyrgios served.

Fans erupted with laughter when Kyrgios aborted his serve a number of times and appeared to be trolling his opponent.

Kyrgios was in scintillating form, giving Australia a 1-0 lead with a 6-2, 6-2 win in an hour and 12 minutes.

It was like a party as Kyrgios joked with teammates and skipper Lleyton Hewitt in Australia's courtside box between games.

But the one-time Australian Open quarter-finalist was deadly serious on court, backing up his pulsating three-set win over Greek superstar Stefanos Tsitsipas on Tuesday night with another classy and composed display.

Mixing under-arm serves with 11 booming aces and an array of dinks and slices, tennis's most charismatic performer bamboozled Norrie while electrifying the crowd with his flamboyance.

Kyrgios wrapped up the opening set in half an hour before grabbing another three service breaks in the second to put Australia in the lead.

Aussies eyeing semi-final spot

Australian No.1 Alex de Minaur can seal the tie with victory over Dan Evans in the second singles rubber, with John Peers and Chris Guccione scheduled to play Jamie Murray and Joe Salisbury in the doubles.

Hewitt suspects the doubles will prove decisive as the inaugural ATP Cup enters the knockout stages.

Hewitt's side have not dropped a match during the pool stages as they look to continue that trend against the Brits.

Led by world No.1 Rafael Nadal, Davis Cup champions Spain also advanced to the last eight with three consecutive 3-0 triumphs during the pool stages.

Seven-times Australian Open champion Novak Djokovic and 2019 US Open finalist Daniil Medvedev helped Serbia and Russia to also progress to the quarter-finals undefeated.

But Hewitt wouldn't swap his world-class Australian No.2 Nick Kyrgios or his unbeaten doubles pairing of Peers and Guccione for anyone and hopes they prove the difference during the "nerve-wracking" climax to the $22 million event.

"Obviously every No.1 is unbelievably strong in the whole competition," Hewitt said.

"No.2's probably vary a little bit from team to team.I'm pretty happy with Nick obviously as No.2

"And when John (Millman) has had to step up, I have full confidence in him as well.

"There's going to be a lot of ties, though, that could potentially come down to the doubles from the quarter-finals onwards as well.

"It's interesting. The doubles in this format, the sudden-death deuce, and also the super-tiebreak, there's a lot of clutch points, which is really exciting for the crowd and TV and the viewers.

"It's pretty nerve-racking, actually, sitting on the sideline and not being able to actually be out there and in control of it."

ATP CUP QUARTER-FINAL LINE-UP:

THURSDAY

10am: Australia v Great Britain

5.30pm: Russia v Argentina

FRIDAY

10am: Serbia v Canada

5.30pm: Belgium v Spain

with AAP