It was only a few hours before when Ivanovic knew she would face Vaidisova - she knew she had a qualifier, but because of Monday's rain-out the final round of qualies was played Tuesday morning, and any of the qualifiers could have been slotted into that spot next to the tournament's No.1 seed.
But it was Vaidisova, a two-time Grand Slam semifinalist and former World No.7, who got drawn into that spot. And Ivanovic looked completely psyched up for it, winning in straights, 6-1, 7-6(4).
It wasn't all plain sailing - after storming out to a 6-1, 3-0 lead in just over half an hour, Ivanovic watched on as Vaidisova brought out some vintage form, winning five of the next six games to go ahead 5-4 and eventually pushing the second set to a tie-break. Ivanovic wrestled control back just in time, though, reeling off four points in a row from 4-3 down to close out the breaker and the match.
"When I saw I was going to play against her I knew it would be a tough match because she's a great player," Ivanovic said of Vaidisova. "She didn't play for a while, and now she wants to play again, and in the second set she was playing really well and making some really good shots out there.
"I'm happy I won the tie-break because you never know what will happen in a third set."
Most of the other seeds in action in the day session advanced, with No.2 seed Sara Errani winning the first 11 games en route to a 6-0, 6-3 win over Lauren Davis, No.3 seed Caroline Garcia fighting nearly two hours for a 7-5, 7-6(5) win over Karin Knapp, No.4 seed Timea Bacsinszky fighting almost two and a half hours for a 7-6(8), 3-6, 6-4 win over Yanina Wickmayer, and No.8 seed Magdalena Rybarikova battling over two and a half hours to scrape past Serbian wildcard Jovana Jaksic, 6-3, 3-6, 7-5.
The night session began with No.5 seed Anastasia Pavlyuchenkova winning 11 games in a row from 6-4, 3-1 down to beat Anna Schmiedlova, 4-6, 6-3, 6-0, improving her career record in Monterrey to 16-0, and then No.7 seed Daniela Hantuchova coming back from the brink of defeat against Monica Puig, saving four match points in the third set - one at 3-5, three at 4-5 - to prevail, 7-6(1), 3-6, 7-5.