High-flying top-ranked star Novak Djokovic, round victories Thursday at the $2.43 million Western & Southern Open, an ATP Masters and U.S. Open Series event.

Djokovic improved to an incredible 55-1 this year with an easy 6-3, 6-3 victory over Czech qualifier Radek Stepanek in 1 hour, 22 minutes on the hardcourts at the Lindner Family Tennis Center. Stepanek was a surprise titlist in Washington D.C. two weeks ago.

The sizzling Djokovic is seeking his sixth Masters title of the year. He beat American Mardy Fish in last week's Masters finale in Montreal.

The Wimbledon and Aussie Open champion and 2010 U.S. Open runner-up Djokovic was the back-to-back Cincinnati runner-up in 2008 and 2009.

The second-seeded Nadal got all he could handle from fellow Spanish left- hander Fernando Verdasco in a 7-6 (7-5), 6-7 (4-7), 7-6 (11-9) marathon on Thursday. The U.S. Open and French Open champion and Wimbledon runner-up Nadal barely prevailed in 3 hours, 37 minutes.

The former top-10 star Verdasco piled up 48 winners, compared to 29 for Nadal, but he also committed 41 unforced errors en route to defeat.

The 10-time Grand Slam champion Nadal, the all-time leader with a whopping 19 Masters titles, is now a perfect 12-0 lifetime against his Davis Cup teammate Verdasco.

Nadal's opponent in Friday's quarterfinals will be a seventh-seeded Fish.

Fish continued his recent fine play with a 7-5, 7-5 victory over 12th-seeded Frenchman Richard Gasquet. The American smacked eight aces en route to the quarters.

The 29-year-old Fish was last week's Montreal runner-up to Djokovic and lost to the great Roger Federer in last year's quality finale here in Cincinnati.

The fourth-seeded Murray, meanwhile, handled American qualifier Alex Bogomolov Jr. 6-2, 7-5 on Day 5. The world No. 50 Bogomolov Jr. stunned Murray at the big Masters event in Miami five months ago.

The Australian Open runner-up Murray captured this Cincinnati Masters tournament back in 2008.

Eighth-seeded Czech Tomas Berdych booked a spot in the quarters by firing 11 aces on his way to blasting ninth-seeded Spaniard Nicolas Almagro 6-2, 6-2 in 64 minutes.

This week's winner will collect $496,000.