Stefanos Tsitsipas had edged passed American Ben Shelton in straight sets to advance to the Round of 16 in the Cincinnati Masters.

It wasn’t easy for the Greek, who had to hard earn his win with a pair of tie-breaks to finish 7-6 (3), 7-6 (2).

Meanwhile in the women’s, eighth seed Greek Maria Sakkari beat Romanian Sorana.

Cirstea (2-6, 6-3, 7-5) to advance to the third round. Sakkari will play Czech Karolina Muchova next.

The 20-year-old Shelton was impressive against the world No.4, who is five years his senior, winning 84 per cent of points behind his first serve but wasn’t enough against Tsitsipas, whose experience saw him go at 93 per cent.

Speaking after the match, the 25-year-old talked about said efficiency and the toughness of the match.

“He’s still relatively young and he has that free spirit in the way he approaches his game,” said Tsitsipas.

“It came down to two tiebreakers and I was very confident if I made a few returns back and got him to rally a bit, things might go my way, and it ended up so. I was tough, for sure. I was tough as nails, and that gave me the win today.

“He hits big, can serve big, so with these kinds of players you have to be 100 per cent there. There isn’t much of a gap that you can give them.”

The win was tough for the fourth seed not just because of his promising up and coming opponent but for a bizarre incident with a spectator.

Tsitsipas was annoyed by a spectator who he alleged was making bee noises and demanded the woman be kicked out.

It took place during the second set where he was seen swatting at the air. He then walked up to the chair umpire and said: “There’s a person imitating a bee behind me.”

“It’s a buzz right before I serve. Do you think that’s okay?”

The frustrated Tsitsipas walked towards a group of patrons to determine who was allegedly making the sound before returning to the umpire to identify the culprit.

“It has never happened in my career.”

“I know they’re supporting (Shelton).

“It’s the lady over there, I want her out. She needs to go.”

The woman was seen apologising to the 10-time title winner.

The Greek star now holds an 11-5 record at the Western & Southern Open, having reached the championship match in 2022.

He will next face Poland’s Hubert Kurkacz on Friday AEST.