SAINT PETERSBURG, Russia (AFP) - Canadian Milos Raonic's reign as St Petersburg Open champion is over after he suffered a second-round defeat to Russian veteran Mikhail Youzhny on Thursday (Sept 22).

Wimbledon finalist Raonic, sixth in the ATP rankings, fired 13 aces but to no avail as 2004 champion here Youzhny battled back from a set down to win 2-6, 7-6 (8/6), 6-4.

Big serving second seed Raonic, who enjoyed an opening round bye, broke twice in the opening set to take it in 32 minutes but Youzhny won the tiebreak in the second to level at 1-1.

In the deciding set, Youzhny, 34, broke in the ninth game to close out his win in two hours 34 minutes.

"It's fantastic!" Youzhny said.

"I'd like to thank St Petersburg fans for their support, which inspired me in the second set when I was trailing 5-1 in the tiebreak.

"Tomorrow (Friday), I await another very hard match. Hopefully I'll manage to recover."

Youzhny will take on Germany's Alexander Zverev, fifth seed here, who beat Daniil Medvedev of Russia 6-3, 7-5, for a place in the semi-finals.

Third seed Czech Thomas Berdych, who returned to action after his withdrawal from the US Open due to appendicitis, scraped into the quarter-finals through a tough three-setter against Russia's Andrey Kuznetsov 6-3, 2-6, 7-6 (7/4).

Berdych, currently ninth in the race to the London ATP Finals - which features the year's top eight players - won the first set with a break in the fourth game but Kuznetsov broke twice in the second to level.

In the third set tiebreak, Berdych was more precise and secured a last-eight spot.

"The result is definitely an improvement from the last year," said Berdych, who lost in the 2015 opening round.

"Today, I faced a very tough opponent and I'm very happy to go through this test."

On Friday, Berdych will face Italian veteran Paolo Lorenzi, 34, who saw off French qualifier Alexandre Sidorenko 7-6 (7/5), 6-4.

Serb Viktor Troicki, seeded seventh, cruised into the last eight with a 6-4, 6-4 win over a compatriot Dusan Lajovic, while eighth seed Joao Sousa of Portugal beat Russian wildcard Andrey Rublev 7-6 (7/3), 6-3, 6-3.