Li was in trouble a few times against Pliskova - she was down a break early in the first set, and after going up 3-1 in the second set she lost three games in a row - but the No.1-seeded Chinese always had things under control, eventually blasting her first ace of the match on match point to win, 63 64.
She still wasn't particularly satisfied with her nine double faults during the match, however.
"At least I could win the last point and stay in the tournament," Li said afterwards. "If you're a tennis player, you'll make double faults. At least I can improve my serve even more from here. I'll talk to Carlos after this, because I didn't get a chance to talk to him yet, we didn't have time to see each other. We will definitely talk about the serve and what I'm doing, and what we can improve moving forward."
Li has never been the No.1 seed at a tournament this big - how does she feel about the pressure?
"I try to feel the same, but it's different," Li said. "It's everything. Before I would come to a tournament as the No.6 or No.7 seed, but now there's a lot more attention and everyone's focused on me.
"But it's not bad. Just a little bit different."
This is Li's eighth time as the No.1 seed at any level of WTA event. She won three of the seven previous tournaments where she was the No.1 seed - Birmingham in 2010 and Shenzhen in 2013 and 2014. She has won 18 of her last 20 matches as the No.1 seed at WTA events and is 23-4 lifetime.
Awaiting Li in the fourth round is Wozniak, who won a streaky match against No.21 seed Anastasia Pavlyuchenkova, 61 67(3) 60. Wozniak served for the match at 6-5 in the second set but got broken, but rebounded in a big way - she dropped just four points in a 20-minute steamrolling in the third set.
Wozniak has had big wins in her career before - her best are three wins over World No.5s, against Serena Williams at Stanford in 2008, Svetlana Kuznetsova at Eastbourne in 2009 and Caroline Wozniacki at Tokyo [Pan Pacific] that year too - but the Canadian is 0-9 against Top 4 players.
Li leads Wozniak in their head-to-head, 2-1, though they haven't played in more than four years.
Pennetta is now 5-0 lifetime against Stosur, though their last two have gone to three sets.