Defending champion Andrey Rublev has been knocked out in the second round of the Monte Carlo Masters by Alexei Popyrin in straight sets.

Unseeded Australian Popyrin overcame sixth seed Rublev 6-4 6-4 and will play compatriot Alex de Minaur next.

"I am feeling really comfortable," Popyrin, 24, said. "[I am] happy to beat a guy who was in form, confident and the defending champ."

Elsewhere, second seed Jannik Sinner is through to the last 16.

The Australian Open champion beat American Sebastian Korda in straight sets - 6-1 6-2 - in his first match on clay this year.

He will play unseeded German player Jan-Lennard Struff on Thursday.

Rublev is the first of the top six seeds to be knocked out but third seed Carlos Alcaraz withdrew on Tuesday because of injury.

Russian Rublev broke to take a 3-1 lead in the second set but Popyrin broke back twice. He then held serve to reach the third round for the first time.

Meanwhile, two-time champion and 12th seed Stefanos Tsitsipas also reached the third round in a straight set win over Argentine Tomas Etcheverry.

Tsitsipas will play fifth seed Alexander Zverev, after the German beat Austrian Sebastian Ofner on Monday.