What Jannik Sinner was overheard saying to his coach about his serve after struggling in Cincinnati

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Returning to defend his Cincinnati title in 2025, Jannik Sinner was made to work hard for his place in the fourth round.

Receiving a bye into round two, Sinner defeated Daniel Galan 6-1, 6-1, in his opener, to set up a third-round clash with Canada’s Gabriel Diallo.

Perhaps unsurprisingly, Sinner raced into a one-set lead against Diallo, 6-2, but didn’t have things quite so easy in the second set.

As the Italian’s serve began to falter, Diallo pushed him all the way to a tiebreaker, where he earned himself a set point.

Unable to convert, Diallo lost to Sinner 2-6, 6-7 [6-8], missing out on a place in the last 16 of the Cincinnati Open.

After the match, Sinner immediately went to the practice courts to work on his serve and was overheard speaking to his coach, Simone Vagnozzi.

Jannik Sinner was heard telling Simone Vagnozzi ‘If you don’t succeed, you’re s—‘ after serving struggles

During the latest episode of ‘TennisMania’, Italian pundit Dario Puppo recalled a conversation overheard between Sinner and Vagnozzi during their late-night practice session in Cincinnati.

“They were practicing that shot. [Simone] Vagnozzi focuses on some details and then says, ‘If you succeed, but when you don’t succeed…'” said Puppo.

“And [Jannik] Sinner says, ‘If you don’t succeed, you’re s—.’ He wasn’t referring to Vagnozzi, obviously, but he says, ‘If I don’t succeed, it’s no good, right?’

“Vagnozzi then says, ‘Oh sure, because you always have to succeed.’ And Sinner says, ‘Exactly.'”

Puppo proceeded to share his thoughts on Sinner’s decision to practice his serve after his third-round match.

“Sinner’s mentality is one that doesn’t want to make a single mistake even in training, and that’s why at the end of the match, despite the time, he absolutely wanted to fix his serve a bit before going back to work on it the next day,” he said.

A lot has been made of Sinner’s serving performance against Diallo, but was it really that bad?

Making just 50% of his 1st serves and hitting five double faults, it’s fair to say Sinner was well below par against Diallo.

However, the world number one is more than good enough to advance regardless of how he performs on serve, as he will now have a chance to make a real step forward in his fourth-round match.

Who will Jannik Sinner play in the fourth round of the Cincinnati Open?

Next up for Sinner is French star Adrian Mannarino, who is enjoying a brilliant tournament at the Cincinnati Open.

• 2025 Cincinnati Open Q1 – Adrian Mannarino defeated Mitchell Krueger
• 2025 Cincinnati Open Q2 – Adrian Mannarino defeated Dalibor Svrcina
• 2025 Cincinnati Open 1R – Adrian Mannarino defeated Jordan Thompson
• 2025 Cincinnati Open 2R – Adrian Mannarino defeated [19] Tomas Machac
• 2025 Cincinnati Open 3R – Adrian Mannarino defeated [13] Tommy Paul

Advancing through qualifying to take down two seeded players, Tomas Machac and Tommy Paul, Mannarino looks dangerous in Mason, Ohio.

He’ll need to be at his best to win his next match, however, as Mannarino will enter the court with a 0-3 record against the 23-year-old Italian.

Sinner’s maiden win over Mannarino was arguably his most memorable, as he defeated him in Bulgaria to qualify for his first career ATP final.

Now a 20-time tour-level champion, with four Grand Slam titles to his name, Sinner is a completely different player from the one who took on Mannarino in Sofia five years ago.

Sinner will take to the court for his fourth-round match in Cincinnati as the heavy favorite, expected to make light work of the French veteran.

If he were to beat Mannarino, Sinner would advance to take on either Felix Auger-Aliassime or Benjamin Bonzi in the quarterfinals.

He won’t want to get too far ahead of himself, however, as Sinner first focuses on Mannarino, who he will play in the fourth round on Wednesday, August 13.