ST. PETERSBURG, Russia (AP) - Top-seeded Mikhail Youzhny of Russia beat Rajeev Ram of the United States 6-1, 6-4 to advance to the quarterfinals of the St. Petersburg Open on Thursday.

Third-seeded Martin Klizan of Slovakia also reached the final eight, beating Simone Bolelli of Italy 6-3, 6-3.

Klizan hit five aces and never faced a break point. He will next play Ricardas Berankis of Lithuania, who advanced when eighth-seeded Jurgen Zopp of Estonia retired with a back injury after losing the first set 6-3.

Earlier, fourth-seeded Fabio Fognini eliminated 2009 champion Serghiy Stakhovsky of Ukraine 7-6 (4), 6-4, while fellow Italian Flavio Cipolla made the final eight with a 6-2, 6-7 (5), 6-3 victory over Grega Zemlja of Slovenia.

Youzhny, the 2004 champion and a two-time runner-up, served hard in the first set and allowed Ram to score only three points on receiving. Youzhny then made a break in the opening game of the second set and held his serve to close the match on his first match point.

``I've opened really strongly and it was enough to win the set,'' Youzhny said. ``It was much easier in the second set after I made a break.''

In his eighth quarterfinal appearance at the tournament since 2001, Youzhny on Friday will face Guillermo Garcia-Lopez of Spain, who was leading 6-1 and 3-1 when Paolo Lorenzi of Italy retired with a left Achilles injury.

Fognini was leading 3-1 and 40-15 in the first set when he made three double faults and Stakhovsky broke him and forced a tiebreaker.

``The tiebreak was really important and I played great the first points,'' Fognini said. ``I went 6-1 and then 6-4.''

He then accelerated to a 5-1 lead in the second set and though the Ukrainian broke for 5-4, Fognini served the match out to love.

He will next face Roberto Bautista-Agut of Spain, who ousted Russia's Teimuraz Gabashvili 6-3, 6-4, while Cipolla will play against Daniel Gimeno-Traver of Spain, who stopped Lukasz Kubot of Poland, 6-4, 7-6 (5).