Jannik Sinner ‘copied’ John Isner’s serve, reveal Jessica Pegula and Madison Keys
Jannik Sinner’s remarkable improvement on serve ‘doesn’t make sense’, according to Jessica Pegula and Madison Keys, with the two WTA stars revealing that the Italian has taken direct inspiration from big-serving former world No 8 John Isner.
The Italian has been the standout player of the 2026 season, compiling a stunning 44-3 win-loss record.
Sinner has won five Masters 1000 titles this year, in addition to reaching the semi-finals of the Australian Open and, most recently, successfully defending his Wimbledon crown.
He leads the ATP Live Race by 1410 points over world No 2 Alexander Zverev and has already secured qualification for the season-ending Nitto ATP Finals.
Despite suffering a shock second-round defeat to Juan Manuel Cerundolo at the French Open, where he struggled in the hot conditions, the improvements in Sinner’s game have been clear to see.
Most notable has been his effectiveness behind both his first and second serves, something that is reflected in the statistics.
Sinner’s service rating over the past 52 weeks on the ATP Tour stands at 302.4, second only to American Reilly Opelka and ahead of the likes of Ben Shelton and Taylor Fritz.
The world No 1 also leads the ATP Tour in service games won (92.9%) and first-serve points won (80.9%).
World No 3 Pegula and Australian Open champion Keys discussed Sinner’s development during an episode of their ‘The Player’s Box’ podcast.
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“His serve is so good, one of the best, most improved shots,” Pegula analysed.
“They should give awards to Sinner’s serve. His serve is a joke. His wide serve on the ad side is insane.
“And every time I watch him, I’m like, ‘Ooh, like I know that’s his favourite serve and it’s like kind of low percentage.’ Like you always think, ‘Oh, there’s no way he’s going for it again.’ Just hits an ace every time.
“I don’t understand. Like how did your serve get so much better?”
Keys then revealed that Darren Cahill, Sinner’s coach, had encouraged the world No 1 to study Isner’s renowned serve and incorporate elements of it into his own game.
“I thought it was pretty crazy because I think I heard Darren talking about it when he first started with Jannik and one of the big things was like we need to improve your serve,” added the American.
“That’s your thing. Basically, pick someone to watch and then just try to copy their serve. And he watched John Isner and was just like, ‘Okay, got it.’”
“And then it’s crazy that when you’re at the top of the game or you’re one of the three at the top of the game to keep improving and being willing to change things when you’re holding 87 consecutive times against people [Alexander Zverev] and someone comes to you like, ‘Yeah, we should make a tweak.’
“The fact that he’s like, ‘Yeah, okay. No problem.’”
Isner later saw the discussion on Instagram and jokingly responded:
“Serving like me with an actual baseline game is a decent combo.”
