MELBOURNE, Australia -- Serena Williams and defending champion Victoria Azarenka, had to withstand the high temperatures in Melbourne to advance at the Australian Open on Thursday.
A dancing Azarenka and an ankle-weary Williams played back-to-back matches, both easy straight-set victories.
Despite the high temperatures, tournament officials left the retractable roofs on both main arenas open because a combination of factors including humidity and court temperature didn't warrant making the venues a temporary indoor haven from the heat.
Ice vests and towels helped players keep their cool, and a women's tour rule allowing a 10-minute break between sets was invoked late in the day, tournament director Craig Tiley said.
"It's always the referee's discretion, but the lack of humidity helped us today," Tiley said. Australia sweltered through a week of record high average temperatures earlier this month, but the first three days of the Open were relatively mild.
Williams went into Thursday's match with an injured right ankle. She didn't seem troubled by the injury, but did finish with a swollen lip after hitting herself with her racket.
"It's OK," she said. "It's a war wound. I think it happens to everyone, but I have never busted it wide open like that. I was like, 'Oh, no. I can't have a tooth fall out.' That would be horrible."
Williams lifted her tempo on the biggest points, including when she finally won an 18-minute game to open the second set en route to a 6-2, 6-0 win over Garbine Muguruza.
"Usually I feel injuries after the match but, so far, so good. I felt pretty much better than I ever dreamed of expecting to feel," Williams said of her ankle.
She later combined with sister Venus to win in the first round of doubles, showing no signs of trouble with the ankle.
The top-ranked Azarenka pranced into Rod Laver Arena for the first match of the day, and said she's starting to find some rhythm after beating Eleni Daniilidou 6-1, 6-0 in 55 minutes.
"I felt like I'm back into the competitive mode," Azarenka said.
The No. 94-ranked Daniilidou only won 10 points in the first set and was shut out in the second despite having triple break point in the fourth game.
Azarenka had her friend and musician RedFoo in the stands watching and signing autographs, and said she went onto the court listening to a "great mix of disco music and a little bit of new music."
The heat didn't seem to bother 42-year-old Kimiko Date-Krumm, who advanced 6-2, 7-5 over Shahar Peer of Israel. She's the oldest woman to win a singles match at the Australian Open.
In the final match of the day -- it finished after midnight -- Britain's Laura Robson outlasted 2011 Wimbledon champion Petra Kvitova 2-6, 6-3, 11-9 in a three-hour match.
The Melbourne-born Robson, who won a mixed doubles silver medal at the London Olympics last year with Andy Murray, trailed 3-0 in the final set before coming back in the match featuring 14 service breaks -- seven by each player. Robson served for the match twice, failing to clinch it at 6-5 before getting another chance nearly an hour later.
Other women advancing included former No. 1-ranked Caroline Wozniacki, No. 14 Maria Kirilenko, No. 16 Roberta Vinci, No. 20 Yanina Wickmayer and Elena Vesnina, who beat No. 21-seeded Varvara Lepchenko of the United States 6-4, 6-2.
Former U.S. Open champion Svetlana Kuznetsova beat 26th-seeded Hsieh Su-wei of Taiwan 6-2, 6-1.
On Friday, the featured women's match will be second-seeded Maria Sharapova's eighth career meeting with Venus Williams.
Sharapova holds a 4-3 edge, although Venus has won both times they've met in Grand Slams -- at Wimbledon.