Maria Sharapova avenged her US Open loss to Anastasija Sevastova to move into the third round of the Australian Open, but Garbine Muguruza became the latest seed to be knocked out.
Latvian Sevastova halted Sharapova's Grand Slam comeback in the fourth round in New York last summer but this time it was the Russian who prevailed 6-1 7-6 (7-4), while Wimbledon champion Muguruza was upset by Hsieh Su-wei.
Sevastova's tricky game wore Sharapova down at Flushing Meadows and the 2008 champion appeared determined not to let that happen again, blasting her way to the first set in just 23 minutes.
The second was much tighter, with Sevastova twice retrieving breaks to force a tie-break, but it was Sharapova who came through.
"I did my job in two sets against someone that's been troubling in the past for me," Sharapova said. "I think I deserve to smile out there after that victory."
Sharapova now faces a third-round clash against 2016 winner Angelique Kerber, who has made an unbeaten start to the season.
Kerber celebrated her 30th birthday with a 6-4 6-1 win over Donna Vekic as she made it an impressive 11 wins in a row to start the season.
Third-seed Muguruza was unable to deal with the unusual game of Hsieh in hot and windy conditions at Melbourne Park and slumped to a 7-6 (7-1) 6-2 defeat.
With the second round still to be completed, nine of the top 16 seeds have already fallen, emphasising the wide-open nature of the women's draw.
Hsieh, who plays with a two-handed slice forehand and likes to give opponents no rhythm, opened up a 5-2 lead in the first set and, although Muguruza fought back to force a tie-break, it was the player from Chinese Taipei who took it.
By midway through the second set, Muguruza looked thoroughly frustrated with herself and the game her opponent was making her play.
She dug in, breaking Hsieh when she served for the match and then saving a match point at 3-5, but two more arrived in the next game and the world number 88 took her chance, holding her arms aloft in delight and disbelief.
US Open finalist Madison Keys was happy to get out of the heat after registering a rapid 6-0 6-1 victory over Ekaterina Alexandrova in just 41 minutes.
"I played well in the first service game and kept it going from there," the 17th seed said. "I'm glad I didn't spend too long out on the heat."
She next faces 104th-ranked Romanian journeywoman Ana Bogdan who is in the third round of a Grand Slam for the first time in her career after beating Yulia Putintseva of Kazakhstan 1-6 6-2 6-3.
Top-seeded Simona Halep cruised to a 6-2 6-2 win over Eugenie Bouchard to keep her quest for a maiden Grand Slam title on course.
"I thought that I played well tonight," said Halep, who dominated the encounter. "I hit the ball really well and it is always tough against her as she hits hard from the baseline."
Sixth seed Karolina Pliskova defeated Beatriz Haddad Maia 6-1 6-1, while eighth seed Caroline Garcia survived a tense clash with teenager Marketa Vondrousova, winning 6-7 (3-7) 6-2 8-6.