The 13th-seeded Wozniacki lost to Su-Wei Hsieh of Taiwan 6-7 (2), 6-1, 6-2. Hsieh lost the first-set tiebreaker but hit her stride in the second and third sets, cruising to a comfortable win over the former world No. 1.
"The first set was not easy, because I just came from Osaka,'' Hsieh said. "When I came on the court ... I was a little bit lost, and she was playing good as well. I asked my coach to come on the court and I said, 'OK, I don't feel anything. I feel weird.' And he said, 'It's OK, just try to play,' and I did. I tried to keep playing and after a couple of games, it was going better and better.''
Hsieh broke Wozniacki's serve six times and saved eight of 10 break points. Wozniacki is 16-14 on the year.
Puerto Rico's Monica Puig defeated the 11th-seeded Kerber 7-6 (5), 5-7, 6-1 in almost three hours.
After failing to convert two match points and dropping the second set, Puig regained her form in the third to oust the three-time Grand Slam winner.
Puig now has a 3-3 lifetime record against Kerber, including a win in the final of the 2016 Rio de Janeiro Olympics.
"We've had so many great matches in the past,'' Puig said. "I have a lot of respect for her. I know it's not over until you go and shake her hand.''
American Christina McHale ousted No. 14 seed Sevastova 4-6, 6-3, 6-3 to advance to the round of 32.