Novak Djokovic didn't get all the breaks against Radek Stepanek on Friday at the Australian Open. The top-ranked Serb, however, remains virtually unbeatable Down Under.

Djokovic beat Stepanek 6-4, 6-3, 7-5 to advance to the fourth round and extend his winning streak to 17 matches at the Australian Open.

Djokovic broke the 34th-ranked Stepanek late in each set but was troubled at times against a wily veteran who mixed up the tempo with a lot of serve-and-volley and some unorthodox shot-making.

"Absolutely it was great. Great match and great fun," Djokovic said. "It's always tricky to play Radek. He's a talented player. Skillful player."

Told about the statistics -- Stepanek won 36 of the 67 points he played at the net -- Djokovic wasn't surprised at all.

"He's skillful on the net, and he was not giving me a lot of rhythm. He was changing up the pace on the ball," Djokovic said. "Nowadays everything is based on the baseline. It's nice to see somebody coming to the net."

Stepanek had Djokovic smiling and acknowledging his winners on some points, frustrated him on others with his constant, stay-in-the-point defense, and even had chair umpire Carlos Bernardes grinning with his over-the-shoulder winner to save one match point near the end.

Djokovic, the two-time defending champion who also won the title at Melbourne Park in 2008, is hoping to become the first man in the Open era to win three consecutive Australian titles.

Angelique Kerber survived some nervous moments before fending off American teenager Madison Keys 6-2, 7-5 in their third-round match, then got to blow out the candles on a cake to celebrate her 25th birthday.

Local organizers brought a cake onto the court for Kerber immediately after the match and the crowd sang "Happy Birthday."

Fourth-seeded Angieszka Radwanska, meanwhile, won her 12th match in a row with a 6-3, 6-1 victory over Britain's Heather Watson.

Sixth-seeded Li Na advanced with a 6-4, 6-1 win over No. 27 Sorana Cirstea of Romania and will next play No. 18 Julia Goerges, who prevented an all-China encounter by beating Zheng Jie 6-3, 1-6, 7-5.

Roger Federer's 6-3, 6-4, 6-4 win over Nikolay Davydenko set Federer on course for a third-round match against Bernard Tomic, the last remaining Australian in the men's or women's draws.

The 20-year-old Tomic beat German qualifier Daniel Brands 6-7 (4), 7-5, 7-6 (3), 7-6 (8).

"I don't think it matters whether he's the last Australian or 10 more," Federer said. "There's always excitement about Aussies playing here. I played him here last year."

Djokovic-Sampras exhibition: Djokovic will team with Pete Sampras to play former Stanford stars Bob and Mike Bryan in a doubles exhibition on March 4 at UCLA's Pauley Pavilion. The pro-set matches will be played before the start of the BNP Paribas Open in Indian Wells.