Rotterdam - Stefanos Tsitsipas' slow start to the year continued as the Greek star suffered a second-round defeat by Slovenia's Aljaz Bedene in Rotterdam on Thursday.

The world number six, who was knocked out of the Australian Open last month by Milos Raonic in the third round, slumped to a 7-5, 6-4 loss in the Netherlands.

Bedene saved five break points before snatching the opening set courtesy of a break in the 11th game, before easing through the second to set up a quarter-final against Canada's Felix Auger-Aliassime.

"He was probably the better player in most of the first set, he was serving really well," Bedene, the world number 52, told atptour.com after beating second-seeded Tsitsipas.

"I stayed focused and it was good towards the end."

Tsitsipas, who won the season-ending ATP Finals last year, now has a 3-4 losing record in 2020.

In-form Russian Andrey Rublev and Gael Monfils, who plays fellow Frenchman Gilles Simon later on Thursday, are the only top-eight seeds remaining in the draw.

Top seed Daniil Medvedev lost to Vasek Pospisil in the opening round, while Italian teenager Jannik Sinner saw off Belgian fourth seed David Goffin 7-6 (9/7), 7-5.

Sinner, who won last year's NextGen Finals in Milan, claimed his first victory over a player ranked in the world's top 10.

"I feel great, especially now in this moment," said Sinner.

The 18-year-old will take on Spain's Pablo Carreno-Busta for a place in the semi-finals.

Results from the ATP tournament in Rotterdam on Thursday (x denotes seeding):

2nd round

Andrey Rublev (RUS x7) bt Alexander Bublik (KAZ) 7-5, 6-3

Gael Monfils (FRA x3) bt Gilles Simon (FRA) 6-4, 6-1

Jannik Sinner (ITA) bt David Goffin (BEL x4) 7-6 (9/7), 7-5

Aljaz Bedene (SLO) bt Stefanos Tsitsipas (GRE x2) 7-5, 6-4