(CNN) -- Former World No.1 Caroline Wozniacki made a shaky start to the new WTA season with a shock defeat to Kazakhstan qualifier Ksenia Pervak in the first round of the Brisbane International Monday.
The Dane finished her 2012 campaign in fine fettle with an 18-3 record after the U.S. Open, but Pervak showed her promise with a 2-6 6-3 7-6 win in two hours 48 minutes.
Wozniacki, watched by her boyfriend, golf's World No.1 Rory McIlroy, powered through the opening set in just 29 minutes, but Pervak hit back to level.
The pair had gone to three sets in their previous two meetings, both won by Wozniacki, but this time the tables were turned.
The eighth seed led 2-0 and 30-0 but Pervak broke back and was dominant in the tiebreak, winning it 7-1 for her first victory over a top ten player.
"It's tough to lose 7-6 in the third -- it could have gone either way, but it didn't go my way today," Wozniacki told the official WTA website.
"I had a good off-season. I've been working very hard. It's just always tough to play your first match of the season," she added.
Wozniacki will now head to Sydney to get in some match practice ahead of the Australian Open, while Russian-born Pervak goes into the second round at Brisbane for the first time in four attempts.
The shocks did not stop there as home hope and seventh seed Sam Stosur was beaten in the night match by Swede Sofia Arvidsson, going down 7-6 7-5.
Fourth seed Angelique Kerber came through in three sets against Georgia's Anna Tatishvili, while her fellow German Sabine Lisicki beat Czech Lucie Safarova 6-2 6-4.
Lisicki will play women's top seed Victoria Azarenka Wednesday.
Serena Williams is already into the second round with a straight sets win over Varvara Lepchenko.
In the men's ATP event, which is headed by Britain's Andy Murray, Japanese fifth seed Kei Nishikori began his campaign with a straights sets 7-5 6-2 win over Australian Marinko Matosevic.