Seeded third this week, Wozniacki won five straight games against the big-serving Vandeweghe from 3-3 in the first set to win that set and take control of the second set. It was eventually settled in a tie-break, where down 4-3 the Dane reeled off four straight points to clinch the 63 76(4) triumph that saw her win just four of 32 points on Vandeweghe's first serve but convert on two of her three break point opportunities. Wozniacki will be aiming for the 400th professional win of her career when she takes on Kristina Mladenovic on Wednesday.
"It was very tough," Ivanovic said. "It was close from the first moment on. She's a very tough opponent, and actually last time we played I lost. So I'm very happy to get the victory tonight.
"The crowd really helped me. I could feel the support. It helped me get through the tough moments."
Also advancing were sixth-seeded Magdalena Rybarikova and eighth-seeded Monica Puig. The Puerto Rican was especially impressive, winning the first 11 games of the match en route to a 52-minute, 60 63 win over Olga Puchkova.
A big upset saw Julia Boserup beat fourth-seeded and 25th-ranked Kirsten Flipkens, 64 16 62. It was the 302nd-ranked qualifier's first WTA main draw win and her first victory over a Top 100 foe.
"I know when I was lower ranked how it was to play against a Top 20 or Top 30 player," Flipkens said. "You have nothing to lose and you go for your shots. She took her chance and played well.