MELBOURNE, Australia - Andrea Petkovic overcame disappointing warm-up form and a run of defeats to Petra Kvitova, holding firm to defeat the No.27 seed 6-3, 4-6, 10-8 in a thrilling first-round upset at the Australian Open.

Coming into the match, the German had lost seven consecutive matches against seeds in Grand Slams, was recovering from a first-round qualifying loss in Brisbane to WTA World No.178 Polina Monova, and had not beaten Kvitova since 2011. However, she came through an epic in two hours and 52 minutes to score her first win over a seed at a Slam since beating Sara Errani in the 2014 Roland Garros quarterfinals, and her first win over a Slam champion since her defeat of Garbiñe Muguruza in the 2016 Doha quarterfinals.

The German admitted she had some mental demons after a frustrating 2017. 

"I had so many tough losses in the Grand Slams last year," she said. "So after I had these match points I tried to stay in the moment. I knew if I got into the spiral of: 'Oh my God, I had match points,' I'd go crazy again.

"I focused so hard and it took all my will power. I think I'm still in that mindset. I didn't even think about what I was supposed to do with the strokes or how I was going to serve. I just thought about not thinking.

"I didn't feel anything. I just existed. I was so in the match. I didn't even realise it was over. I have no feelings whatsoever about this - in a good way.

"I'm going to try and stay like this and not get too euphoric. If it was the final, I'd be running naked around Melbourne Park probably and jumping into things. But it's not, so I'm trying to keep the euphoria for later and stay focused for the next match."

In a match mainly characterised by short, snappy points, the former WTA World No.9 was the fastest out of the blocks, taking both of her break point opportunities efficiently in racing out to a 5-1 lead. Kvitova was generous with her gifts - over the course of the match, she would commit 65 unforced errors and 10 double faults. 

However, Petkovic was also sharp on return in particular: despite landing a decent 72% of her first serves in the opening set, the Czech won only 50% of the points behind what is usually a formidable weapon. A belated surge in form from the Czech in the closing stages of the set made the scoreline more respectable but wasn't quite enough to save it, as Petkovic maintained her 100% break point conversion rate to capture her opponent's delivery for a third time.

But the 2012 semifinalist had found momentum of sorts now, paving the way for a solid second set from both players in which both dominated on serve. The first eight games saw just one break point - on the Petkovic serve in the third game, saved by a service winner - while rallies were in short supply. The few extended points tended to be played relatively conservatively, with both players reluctant to open up any angles for their opponent.

At 4-4, Petkovic blinked - and Kvitova struck. A double fault from the WTA World No.98 put her down 0-30, and a ferocious groundstroke winner from Kvitova sealed the break. The set's drama wasn't quite done - but the 27-year-old was able to survive eight break points to serve it out in the following game, thanks to a combination of timely service winners and some surprising errors from Petkovic.

Despite these missed chances, the deciding set saw the 2011 quarterfinalist bounce back in stellar fashion to take a 4-0 lead. Once again, Petkovic's serve was a bedrock, and she was unthreatened in her first two service games of the set. By contrast, Kvitova conceded a first break with a double fault, and then lost out in a three-deuce tussle to go down another break as her groundstrokes went awry once more off both wings. The former WTA World No.2 also seemed to be feeling the heat, crouching over between points.

Just as in the first set, the two-time Wimbledon champion rallied, retrieving the first break as Petkovic produced a variety of groundstroke errors of her own - and the second by peaking with a flurry of spectacular winners, including a brilliant inside-out backhand.

With the quality from both players going up a level as the match reached its climax, Kvitova once again demonstrated the best of both her talent and her determination to save three match points at 4-5, two with clean backhand winners, before levelling the match with a magnificent forehand down the line that skidded into the corner of the court.

"I maybe could have done a little more. But she played a few really good points on match points," Petkovic admitted.

Now in full flow, the Czech surged into the lead for the first time in with a swashbuckling drive volley to go up 6-5.

Petkovic's response was to up the ante on return, and an ill-timed ninth double fault put the brakes on the Kvitova renaissance to send the match into extra time. With the tension building, the No.27 seed pounced again at 7-7 following a handful of errant Petkovic forehands - but once more was unable to close it out, with another netted groundstroke enabling the German to level at 8-8.

Continuing to crouch over between points, Kvitova once more lapsed into errors, particularly at net - and her opponent, who had maintained her composure admirably, didn't need another chance. A spectacular pass got Petkovic into Kvitova's final service game - and she sealed one of her finest wins in recent years as the Czech delivered a tenth double fault.

"I had two chances to serve it out," Kvitova said. "But it was very difficult serving from that end because it was into the wind.

"It was a great match and in the end I'm happy because I was able to play."

Meanwhile, after close to three hours on court, the German summed things up nicely by saying: "Sometimes you have to hit your head against the brick wall until it breaks down."

Petkovic will have the opportunity to progress beyond the second round of the Australian for just the second time in her career when she faces either Jana Cepelova or Lauren Davis on Thursday.