Former world No.1 Caroline Wozniacki's fall from grace has continued with a disappointing first-round exit from the Australian Open.
The two-time grand slam finalist went down 1-6, 7-6 (7-3), 6-4 to Kazakhstan youngster Yulia Putintseva on Monday. The defeat leaves the Dane in danger of dropping out of the world's top 20. 
Serena Williams survived a tough early test to safely progress to the second round. The 21-time grand slam champion scored a 6-4, 7-5 win over Italian Camila Giorgi.
A knee injury had prevented Williams from completing a competitive match since the US Open in   September, but the American came through unscathed to book a second-round meeting on Wednesday with either Latvian Jelena Ostapenko or Taiwan's Su-Wei Hsieh.
"It wasn't very easy. She obviously plays very well and knows how to play the shots," Williams said. "I haven't played a competitive match in a long while but it was really good. It wasn't quick so that worked to my advantage. I was able to stay in it and stay calm today and that's what matters most." Williams broke Giorgi twice in the opening set but couldn't crack the highest-ranked unseeded player in the draw again until the 11th game of the second set when the Italian double-faulted on game point.
The top seed didn't need a second invitation to close out the match, finishing the contest with her ninth ace to preserve her record of never having lost in the first round in 15 visits to Melbourne Park. Earlier, two-time Wimbledon champion Petra Kvitova also dispelled any lingering fitness doubts to be the first player through to the second round. The sixth seed scored a commanding 6-3, 6-1 win over Thai qualifier Luksika Kumkhum. Kvitova pulled out of last week's Sydney International with gastro, having also retired mid-match during the first round in Shenzhen earlier this month.
Kvitova next plays Daria Gavrilova on Wednesday for a place in the last 32 after Australia's rising star ousted Czech Lucie Hradecka 7-6 (6-3), 6-4 in her opener.
In other women's matches, Spanish 10th seed Carla Suarez beat Swiss qualifier Viktorija Golubic 7-5, 6-4 and American Nicole Gibbs defeated Czech Klara Koukalova 6-2, 2-6, 6-1.