Novak Djokovic is tough to beat at Wimbledon, indoors or out.

Playing the day’s first Centre Court match yesterday under the retractable roof, defending champion Djokovic rallied past Radek Stepanek 4-6, 6-2, 6-2, 6-2.

When a drizzle delayed the start of the third round, tournament officials decided Djokovic’s match should be played inside. An odd spectacle ensued: The roof closed as the sun came out and outside court covers came off.

The No. 1-ranked Djokovic missed opportunities to seize an early lead, failing to convert his first five break-point chances before he lost serve at love to drop the opening set. But he dominated from there, breaking in the first game in each of the final three sets.

Also advancing to the second week was top-ranked Maria Sharapova. She rallied from a break down in the second set to beat Hsieh Su-wei 6-1, 6-4.

American Sam Querrey hit the last of his 21 aces on match point and beat No. 21-seeded Milos Raonic, 6-7 (3), 7-6 (7), 7-6 (8), 6-4. That second-round match had been suspended in the third set Thursday because of rain.

Kim Clijsters led 6-3, 4-3 when No. 12 Vera Zvonareva retired struggling with a cough. The unseeded Clijsters, who plans to retire after the U.S. Open, is a four-time Grand Slam seeking her first berth in a Wimbledon final.

Americans Sloane Stephens and Christina McHale were eliminated in the third round. The 19-year-old Sloane Stephens was beaten by Sabine Lisicki 7-6 (5), 1-6, 6-2, and the No. 28-seeded McHale lost to No. 8 Angelique Kerber 6-2, 6-3.

No. 3 Agnieszka Radwanska defeated Britain’s Heather Watson under the roof, 6-0, 6-2.