The first attempt at 3-1 in the first set against unseeded Lajovic might have been regarded as text-book execution, if there existed such a consensus.
With the Serb standing well behind the baseline, Kyrgios leant over the ball, bounced it a few times and without looking up, flicked it just over the net.
It landed with enough slice to bounce twice for an ace and seal the game, leaving a flat-footed Lajovic no chance to reply.
More casually struck, Kyrgios’s second effort lacked something in execution, allowing Lajovic to swoop in and easily make the retrieve.
But the Australian was ready for the Serb’s drop-shot return, and flicked it past him to close out the first set.
British tennis luminary Judy Murray thrilled in the tactic.
“The whole point of tennis competition is to disrupt (yo)ur opponents game by applying pressure through changing the speed, spin, direction, depth or height of the ball,” the former Fed Cup captain and mother of Andy Murray tweeted.
“And that includes the serve. Kyrgios is a genius. I’m surprised more players don’t do it.”
Belgian professional Kirsten Flipkens was among the social media users backing Murray’s stance, but there were plenty of detractors denouncing under-arm serving as questionable sportsmanship.
The debate between the laws and “the spirit” of the game is not unique to tennis, with a number of other sports having their own taboos.
Cricket was in uproar on Tuesday after Indian bowler Ravichandran Ashwin ran out English batsman Jos Buttler with the rarely used but entirely permissible “Mankad” dismissal in the Indian Premier League match on the previous evening.
As an Australian, Kyrgios will be well aware that a ball delivered underarm in a cricket match in 1981 triggered one of the biggest sporting scandals in the country’s history.
Australia’s Trevor Chappell rolled the ball along the pitch to prevent New Zealand batsman Brian McKechnie from scoring enough runs to win a match. It was perfectly legal at the time, but universally condemned.
In tennis, the frowning of opponents and conservative fans has likely made most players think twice about taking up under-arm serving as a tactic.
Five-times Grand Slam champion Martina Hingis was jeered vociferously by the crowd during the 1999 French Open final when she tried it against Steffi Graf on the way to defeat.
Roger Federer, however, said another concern was simply looking silly.
“Shouldn’t be ashamed if you try it. Just look silly if you miss,” the Swiss Master said after Kyrgios’s effort against Nadal.
For a maverick like Kyrgios, who regularly squanders points on botched ‘tweeners and other trick shots, the threat of embarrassment is unlikely to be a deterrent.