Reigning champion Novak Djokovic moved into the fourth round at The Championships, Wimbledon.

The world No. 1 star dropped the first set against Czech veteran Radek Stepanek on Friday before charging back for a 4-6, 6-2, 6-2, 6-2 victory over his 28th-seeded counterpart under the roof on Centre Court at the All England Lawn Tennis Club.

Morning rain caused a delay and prompted officials to close the translucent covering over tennis' most famous court, but it was not raining when Djokovic took to the court.

"I was a little bit surprised, when I saw sunshine, that the roof is closed," Djokovic said. "Obviously they're relying on a forecast that I don't think is very reliable here. But OK."

The high-flying Djokovic advanced in 2 hours, 49 minutes and broke the 33- year-old Stepanek seven times while getting broken only once and smacking nine aces.

"I was a set down but managed to make the crucial break in the opening game of the second set," Djokovic said. "And then I thought I played really well."

The Serbian star is now 30-1 over his last five majors and 42-2 over his last seven Grand Slams.

The 25-year-old Djokovic reached his first-ever Wimbledon final and captured his first-ever title here with a victory over Rafael Nadal a year ago. Nadal beat Djokovic in the French Open final 18 days ago, but the mighty Spaniard will not appear in a sixth straight Grand Slam title match after being shocked by 100th-ranked Czech Lukas Rosol under the roof on Centre Court Thursday night.

Djokovic's round-of-16 opponent on Monday will be will fellow Serb Viktor Troicki, who upended 15th-seeded Argentine Juan Monaco 7-5, 7-5, 6-3 on Day 5 of this fortnight.

A top-10 upset occurred when 26th-seeded Russian veteran Mikhail Youzhny dismissed eighth-seeded Serb Janko Tipsarevic, 6-3, 6-4, 3-6, 6-3. Youzhny is into the Wimbledon round of 16 for a seventh time, but has yet to reach a quarterfinal at the AELTC. Tipsarevic plays his worst tennis on grass, including losses in the first or second round here the last four years.

Nifty 18th-seeded Frenchman Richard Gasquet still has yet to drop a set after upending 12th-seeded Spaniard Nicolas Almagro 6-3, 6-4, 6-4, while Belgian veteran Xavier Malisse also posted a third-round upset by tackling 17th-seeded Spanish lefthander Fernando Verdasco in five sets, 1-6, 7-6 (7-5), 6-1, 4-6, 6-3. Gasquet was a Wimbledon semifinalist in 2007. while the once- promising 31-year-old Malisse reached the Wimbledon final four 10 years ago.

The second round concluded Friday when 6-foot-6 American Sam Querrey surprised rising 21st-seeded Canadian slugger Milos Raonic 6-7 (3-7), 7-6 (9-7), 7-6 (10-8), 6-4 in a match that was completed Friday after being suspended because of darkness on Thursday. The two players combined for 46 aces, including 25 from Raonic.

Querrey will meet 16th-seeded Croat Marin Cilic on Saturday.

Another third-round result saw Uzbekistan's Denis Istomin pop 16 aces and dismiss Colombian Alejandro Falla 6-3, 6-4, 3-6, 7-6 (7-5). Istomin will encounter Youzhny on Monday.