MELBOURNE, Australia — Novak Djokovic absorbed plenty of pressure from Radek Stepanek before advancing to the fourth round of the Australian Open, then unleashed some stinging shots at Lance Armstrong after the doping-tainted cyclist’s long-expected confession.

Djokovic broke the 34-year-old, 34th-ranked Stepanek late in each set of a 6 -4, 6-3, 7-5 win Friday, extending his winning streak to 17 matches at the Australian Open.

In the next match on Rod Laver Arena, Maria Sharapova beat Venus Williams 6-1, 6-3 in an unexpectedly lopsided third-round result.

Williams could consider herself fortunate — Sharapova’s opponents in her first two matches failed to win a game from the Russian star.

Three matches into this tournament, and Sharapova, who pumped her arms six or seven times after she served out with an ace, has lost just four games heading into her fourth-round match against unseeded Belgian Kirsten Flipkens.

“I think when we both looked at the draw, it was a matchup we were both looking forward to,” Sharapova said of Williams. “She’s a tremendous athlete and a great champion.”

At Djokovic’s post-match news conference, the questions quickly turned from tennis to Armstrong’s confessions about doping in cycling during his television interview with Oprah Winfrey in the U.S. Thursday night.

“I think it’s a disgrace for the sport to have an athlete like this,” said Djokovic, the No. 1-ranked man in tennis. “He cheated the sport. He cheated many people around the world with his career, with his life story.”

Djokovic, who has five Grand Slam titles, said the doping program in tennis was sufficient to catch the cheats, though he conceded he hasn’t had a blood test that could detect illegal oxygen-boosting agents for six months.

He will play No. 15 Stanislas Wawrinka, who beat American Sam Querrey 7-6 (6), 7-5, 6-4 on Friday, in the fourth round.

Querrey’s loss meant that for the second consecutive year, there will be no American men in the fourth round at Melbourne Park. Last year was the first time no U.S. man reached the fourth round since 1973.