What In the world is going on with Andrey Rublev?

Defending champion Andrey Rublev was knocked out of the Monte Carlo Masters in a 6-4 6-4 second-round loss to Australian Alexei Popyrin on Wednesday, and world No. 2 Jannik Sinner eased through his first test.

Popyrin broke in the third game of the first set, but Rublev broke to take a 3-1 lead in the second, only for the Australian to hit back immediately.

A further break made it 5-4 to Popyrin, and he held serve to reach the third round for the first time. Russian fifth seed Rublev had received a bye into the second round.

“The idea was not to give him the same ball,” Popyrin said.

Alexei Popyrin moves on after getting past defending champion Andrey Rublev in the second round of the Monte Carlo Masters on Wednesday. Photo by Julian Finney (Getty Images)

“He is probably the best player from the baseline when you give him rhythm, so I tried to change the pace, height and spin and I think it worked really well for me today.”

Popyrin will face fellow Australian Alex De Minaur next, after the 11th seed beat Dutchman Tallon Griekspoor 2-6 6-2 6-3.

Prior the match, Andrey Rublev admitted his controversial Dubai default could have “stuck in my mind” following a poor run of form since the incident.

World No 6 Rublev was disqualified from his semi-final match against Alexander Bublik at the Dubai Tennis Championships while trailing 5-6 in the deciding set, after appearing to swear directly at a line judge.

Since the incident at the beginning of March there has been a noticeable drop in his form, with the Russian failing to make any impact across the Sunshine Double.

He suffered a comprehensive 6-4, 6-4 defeat to Jiri Lehecka in the third round at Indian Wells, before losing his opening match in Miami to Tomas Machac by the same scoreline.