Clijsters only needed 47 minutes to beat Stephanie Foretz Gacon of France 6-0, 6-1 on Wednesday, conceding just 10 points in the first set and showing no signs of a hip problem that forced her to retire during a semifinal against Daniela Hantuchova at a warmup tournament two weeks ago.
She will meet Hantuchova in the next round here, and has a potential rematch of the 2011 Australian Open final with Li Na in the fourth.
Roger Federer, who has won four of his 16 Grand Slam titles in Australia, got a walkover into the third round when Andreas Beck of Germany withdrew from their scheduled Hisense Arena match due to a lower back injury. It deprived Federer of a different view at Melbourne Park, where he has played every match in Rod Laver Arena since the third round of the 2004 Australian Open. He'll meet either Ivo Karlovic of Croatia or Carlos Berlocq of Argentina in the next round.
Eighth-ranked Mardy Fish became the first top 10 player on the men's side to lose, falling 7-6 (4), 6-3, 7-6 (6) to Colombia's Alejandro Falla.
No. 7 Tomas Berdych advanced 6-1, 6-0, 7-6 (4) over Olivier Rochus of Belgium and Philipp Kohlschreiber of Germany was leading 6-0, 4-0 when Spain's Pere Riba retired with an injured left foot.
Taiwan's Yen-hsun Lu beat French qualifier Florent Serra in straight sets and No. 30 Kevin Anderson of South Africa beat Sergiy Stakhovsky of Ukraine 3-6, 6-1, 7-6 (3), 6-3.
Clijsters and No. 20 Hantuchova, a 4-6, 6-4, 6-3 winner over Lesia Tsurenko, have been playing each other for years.
"When the injury happened, it happened against Daniela," Clijsters said of the hip muscle spasms she had at the Brisbane International. "She's been playing well this season so far.
"We both go back a long way — we grew up playing under-14s together. Now almost 30 — still battling it out."
This was Clijsters best run at a major since the last Australian Open — she lost in the second round at the French Open and didn't play Wimbledon and the U.S. Open.
Li is also returning to form, going further than she has a Grand Slam tournament since her breakthrough win at the French Open. She next plays No. 26 Anabel Medina Garrigues of Spain, who beat Olga Govortsova of Belarus 6-1, 6-0.
Li said she loved being back on Rod Laver Arena, where she burst onto the global tennis scene last year, while Clijsters still clearly feels at home on a court where she's still known as "Aussie Kim" long after her relationship with Lleyton Hewitt ended.
In a post-match TV interview, she asked presenter Rennae Stubbs a favour, saying her brother-in-law phoned her from Belgium to ask if she could convince the crowd to sing a birthday song for Elke, Clijsters' younger sister.
The crowd obliged, after Clijsters kicked it off.
Li took longer for her second-round win, saying it was harder than the scoreline suggested. She also has fond memories of Melbourne
Her form dipped after the French Open, with losses in the second round at Wimbledon and the first round at the U.S. Open, until she returned to Australia.
Coming off a run to the final at last week's Sydney International, Li was the first woman into the third round.
Li, who will be 30 next month and is seeded No. 5 at Melbourne Park, said she had great memories of the start of 2011.
"I'm feeling always good to come back to Rod Laver Arena," she said, reflecting on how her life had changed dramatically since last season started. "This year is much better than last year — more fans come to watch me play, not only from China but all over the world."
Li's Chinese compatriot, 16th-seeded Peng Shuai, lost 6-2, 6-4 to Iveta Benesova of Czech Republic, while former No. 1-ranked Jelena Jankovic beat Chang Kai-chen of Taiwan 6-4, 6-2.
Serena Williams advanced to the second round in a match that finished after midnight, her ankle holding up to its first test since she sprained it in Brisbane two weeks ago. The only thing that bugged her, despite the 11:32 p.m. start on Tuesday, were the insects in a 6-3, 6-2 win over Tamira Paszek.
"I hate bugs more than you can imagine," Williams said. "Like, they kept jumping on me. Yuck!"
Between points, Williams picked up and moved or shooed away bugs that landed on court, and two that landed on her back. A big one gave her a fright, making her hop as she tried to stifle a screech.
"I'm going to request not to play at night anymore because I hate bugs, except for the final. I heard it's at night," Williams said. "I'll try to get used to them."
Two years after she won her last Australian Open title, Williams extended her winning streak to 15 matches at Melbourne Park in the season's first major tournament. She won titles in 2009 and 2010 but missed the chance to defend her title last year amid a prolonged injury layoff.
Williams was playing only her third match since losing the U.S. Open final to Sam Stosur last September, so she admitted being "a wee bit tight." Wimbledon champion Petra Kvitova and No. 4-ranked Maria Sharapova also advanced.
Stosur didn't make the second round, losing 7-6 (2), 6-3 to No. 59-ranked Sorana Cirstea, but fans hung around to watch another Aussie hope. Hewitt, a two-time major winner, gave the night session crowd something to cheer when he beat Cedrik-Marcel Stebe of Germany 7-5, 6-4, 3-6, 7-5, winning the last six games to overcome two service breaks in the last set.
Hewitt's win put him into a second-round match against old rival Andy Roddick.
Defending champion and top-ranked Novak Djokovic won the last 17 games to beat Paolo Lorenzi of Italy 6-2, 6-0, 6-0. Both the men he has beaten in Australian finals also advanced. Andy Murray, runner-up the last two years, defeated American teenager Ryan Harrison 4-6, 6-3, 6-4, 6-2. Sixth-seeded Jo-Wilfried Tsonga, beaten by Djokovic in the 2008 final, eliminated Denis Istomin 6-4, 3-6, 6-2, 7-5.