Azarenka played almost flawless tennis in the first set, needing just 31 minutes to take it at love, but from the start of the second set the story was much different. Wozniacki came out swinging, racing out to a 3-0 lead, and even though Azarenka got back on serve, Wozniacki came close to breaking again, holding six break points up 4-3 for a 5-3 lead - Azarenka hung tough and fought them all off, though.
In the end Azarenka closed in too fast, closing out the No.5-seeded Wozniacki, 6-0, 6-4.
"First of all, thank you guys so much for staying and supporting us," Azarenka said in her on-court interview, referring to the lengthy rain delay that pushed the night match's start time past 9pm. "I know that it's been a little bit of a long night for everyone, but I really want to thank you all so much.
"I felt like the first set I was playing really, really well, and executing my game. She's the type of player you just can't beat 6-0, 6-0 though - you know she's going to turn it up. She started playing more aggressively in the second set and it was definitely getting tougher and tougher out there.
"But I stayed strong and stayed aggressive, and I was able to turn it around in the end."
Garcia's win over the World No.4 was the first Top 5 win of her young career. Before this she'd had four wins over World No.6s - Agnieszka Radwanska once, Ana Ivanovic three times - but never a Top 5.
Other seeds moving through were No.7 seed Lucie Safarova, who got revenge on American wildcard CoCo Vandeweghe for a loss at Wimbledon, 6-4, 7-5, No.8 seed Karolina Pliskova, who beat Hungarian qualifier Timea Babos, 6-4, 7-5, No.14 seed Elina Svitolina, who survived Eugenie Bouchard at night, 7-6(6), 7-5, and No.15 seed Andrea Petkovic, who downed Camila Giorgi, 5-7, 6-3, 6-3.
Notable winners among the unseeded match-ups were Belinda Bencic, who stretched her win streak to eight matches with a 6-1, 6-4 win over Flavia Pennetta, Jelena Jankovic, who edged Madison Keys, 7-6(4), 6-4, and Sloane Stephens, who rallied to beat German qualifier Mona Barthel, 3-6, 7-6(1), 6-2.