O'Connell started strongly in the blustery conditions, surging into a 3-1 30-0 lead before being pegged back by Sinner, who won four consecutive points to avoid going down by a double break.

The Italian then reeled off five of the next six games to take the first set in 58 minutes against his Australian opponent, who showed an impressive variety of shots as he tried to force his way back.

Dropping his serve in the first game of the second set, O'Connell struggled to maintain his challenge as Sinner stepped up the pressure, the world No.3 going on to settle the match 6-4 6-3.

"Today was ... much more windy, so I had to adjust a little bit," Sinner said.

"He started off really well, I made a couple of mistakes.

"When you are a break down especially in the beginning, it's always tough.

"(But) I had some chances even before I broke him, so I know that I was doing the right things.

"I tried to serve really solid. He made a couple of mistakes in important moments (which) today was the key."

Sinner - who has now equalled ATP Tour-leader Alex de Minaur with 19 wins in 2024 - will next meet Czech Tomas Machac, who progressed to the quarter-finals with a 6-3 6-3 victory against Matteo Arnaldi of Italy.

De Minaur takes on Hungary's Fabian Marozsan later on Wednesday (AEDT).

Daniil Medvedev took another step towards retaining a title for the first time in his career, beating Germany's Dominik Koepfer 7-6 (7- 5) 6-0 to reach the last eight.

The Russian third seed overcame a shaky start and converted four break points while dropping serve just once to progress without dropping a set.

"Sometimes it happens when you lose the first set the way he lost ... it brings your (opponent's) energy down," Medvedev said after collecting his 350th career win.

The Russian faces Chile's Nicolas Jarry - who beat seventh seed Casper Ruud of Norway 7-6 (7-3) 6-3 - in the last eight.

Top-seeded Carlos Alcaraz also advanced with ease in a 6-3 6-3 win over No.23 seed Lorenzo Musetti.

Alcaraz, who beat Musetti in less than 90 minutes and looked as comfortable as ever on the court, said he's "probably" playing his best tennis since last summer. That ankle injury from last month is no longer a concern, he said.

"I don't know if this is the best game that I'm playing, but without a doubt it's the best feeling," the Wimbledon champion said.

"I'm feeling great on the court. I'm moving great. ... I'm not thinking about the ankle anymore on the court."

Alcaraz faces No.11 seed Grigor Dimitrov in the quarter-finals after the Bulgarian beat No.8 seed Hubert Hurkacz 3-6 6-3 7-6 (7-3).

- with Reuters

Australian Associated Press