The No.6-seeded Wozniacki was the first of the pair to advance, needing an hour and seven minutes to outrally Chanelle Scheepers in the first match of the night session on Arthur Ashe Stadium, 61 62.
"I felt pretty good," Wozniacki said afterwards. "I really like playing the night session on Ashe. It's great. It's a nice atmosphere. It's very electric. I was really excited to go out there and play today."
Wozniacki wasn't the only Top 8 seed to move through, with No.7 seed Petra Kvitova beating Bojana Jovanovski, 62 64; No.8 seed Angelique Kerber grinding out a two-hour, 46-minute win over Eugenie Bouchard, 64 26 63; No.9 seed Jelena Jankovic ending the comeback major of Alisa Kleybanova, 63 62; and No.10 seed Roberta Vinci battling back from a set down to beat Lucie Safarova, 46 61 62.
"I'm very happy I won this close match," Kerber said of her win over Bouchard. "She was playing very well from the first point to the last. She is a very young and talented player and it wasn't easy for me until the last point. I needed to give everything I had today. I'm very happy I'm in the third round."
"It was not easy conditions today - it was a little bit gusty - but I was very happy overall," Ivanovic said. "Alexandra's a tough player. She played well and strikes some really good backhands. I was really happy I managed to push the ball to her to the forehand - she made a few more errors on that wing."
No.14 seed Maria Kirilenko, No.16 seed Sabine Lisicki, No.21 seed Simona Halep, No.24 seed Ekaterina Makarova and No.25 seed Kaia Kanepi also won, with Lisicki beating Paula Ormaechea, 62 63, her first time winning back-to-back matches since suffering a right wrist injury after Wimbledon.
"I didn't spend as much time on court after Wimbledon because I had to take care of a little injury, but I did the best I could, and every match is getting better and I'm getting happier with the way I play," Lisicki said. "I took my time. I knew out of experience if you don't take your time to cure it, it might take over. I wanted to make sure everything was fine with it so I'm pain-free when I come back."
The day wasn't without its upsets though, the biggest surprise of them all being No.19 seed Sorana Cirstea going out to Japanese qualifier Kurumi Nara, 75 61. Also, Karin Knapp took out No.22 seed Elena Vesnina, 61 64, and American wildcard Alison Riske beating No.28 seed Mona Barthel, 64 62.