Venue: Melbourne Park Date: 18-31 January
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Ivanovic has slipped down the rankings over the last 18 months
Argentina's Gisela Dulko beat former world number one Ana Ivanovic of Serbia in a dramatic second-round match at the Australian Open.
Dulko won 6-7 (6-8) 7-5 6-4, despite seeing a double break disappear in a final set of incredible tension.
Defending champion Serena Williams and her older sister Venus both had straight-sets victories.
Fourth seed Caroline Wozniacki and seventh seed Victoria Azarenka enjoyed swift straight-sets wins.
Denmark's Wozniacki saw off German Julia Goerges 6-3 6-1, and Azarenka of Belarus beat Switzerland's Stefanie Voegele 6-4 6-0.
Serena Williams swept past Czech Petra Kvitova 6-2 6-1 after Venus had earlier powered her way into the third round with a straightforward 6-2 7-5 win over Austrian Sybille Bammer.
"Today I was better than my first round match, I was moving better, better energy. All round a lot better," said Serena.
Venus, who went out at this stage last year to unheralded Spaniard Carla Suarez Navarro, said of Bammer: "She's a really good player and a really good athlete.
"Her game is a little bit different from most people, so you really have to be a little more patient because she's hitting a kind of a moonball almost.
"It's a little bit different, so I just had to just make sure I stayed on my rhythm - I'm happy to be through."
She will now play either Croatia's Karolina Sprem or Australian Casey Dellacqua in the third round.
Ivanovic reached number one in the world when she won her first Grand Slam title at the French Open in 2008 but has since slipped to 21 in the rankings.
I do feel better on the court. I'm playing much better. I feel like my old self
The 22-year-old struggled desperately on serve against Dulko, who edged home despite clearly suffering from nerves herself as she let a 5-1 lead slip in the final set.
After battling back to 5-4 down, Ivanovic double-faulted twice while trying to level and Dulko clinched victory on her sixth match point.
"It's hard. It hurts, I must say," Ivanovic admitted. "For sure it will, but it's a process. I do feel better on the court. I'm playing much better. I feel like my old self.
"There are still some areas that are not there for me to rely on. I just have to sort of keep my head up and try to improve, work."
Russia's ninth seed Vera Zvonareva thrashed Czech Iveta Benesova 6-0 6-3, Polish 10th seed Agnieszka Radwanska beat Russian Alla Kudryavtseva 6-0 6-2, and 13th seed Sam Stosur pleased the home fans with a 7-5 6-3 win over Kristina Barrois on Rod Laver Arena.
There was doubles success for the British women, with Elena Baltacha, Laura Robson and Sarah Borwell all enjoying victories.
Baltacha teamed up with Latvian Liga Dekmeijere to beat Lucie Safarova and Aleksandra Wozniak 7-5 6-2, and Borwell and American Raquel Kops-Jones saw off Petra Martic and Polona Hercog 6-4 7-6.
Robson, celebrating her 16th birthday, joined up with Australian Sally Peers to defeat Jill Craybas and Abigail Spears 6-3 7-5.
"They (the crowd) get into it," said Robson. "At Wimbledon they certainly don't make chants up for every change of ends.
"It was pretty interesting. I was handed a certificate to sign to be an Australian as well but they said if I wanted my birthday present I had to sign it, so I didn't."