Former Wimbledon champion Petra Kvitova suffered a shock exit from the Australian Open as she was ousted 6-2 1-6 6-4 by Luksika Kumkhum.
The sixth seed must have fancied her chances of progressing after being paired against the world No 87 from Thailand.
However Kvitova got off to a terrible start on Margaret Court Arena as she broken twice en route to losing the first set 6-2.
The Czech seemed to have weathered the storm, though, as she levelled matters in impressive fashion - breaking Kumkhum three times as she won the second set 6-1.
However, Kumkhum refused to give up and worked her way into a winning position as she led 5-3 and served for the match.
Kvitova managed to break back but she then threw all the hard work out the window as dropped her serve to hand Kumkhum victory - and a place in the second round against Mona Barthel.
"I'm very excited to beat the number six player in the world," Kumkhum said. "Today is a great day for me, I am very happy."
Kvitova could offer little explanation for the loss, saying: "I really want to know what happened out there. Unfortunately I didn't play well. I didn't play my game that I really tried all off season to work on.
"It was a great off season. I was really excited to be here, feeling good. But I think that probably I wanted it too much, and then everything just fell down."
Elena Vesnina, the No 23 seed, also suffered an upset as she went down 6-2 6-2 to Alison Riske.
The 15th-ranked Sabine Lisicki had no such problems, though, as she breezed past Mirjana Lucic-Baroni 6-2 6-1.
Serena Williams, the top seed, was also a 6-2 6-1 winner with the American crushing teenager Ashleigh Barty in just 57 minutes.