Li broke Pliskova in the fourth game of the first set to lead 3-1, but the 241st-ranked Pliskova broke back to force a tiebreaker. Li broke once in the second set to close out the indoor hard-court match.
Fifth-seeded Julia Goerges hit six aces on the way to beating Stefanie Voegele 6-2, 6-4.
Other seeded players advancing included No. 7 Klara Zakopalova and No. 8 Angelique Kerber. Zakopalova defeated Rossana De Los Rios 6-3, 6-7 (6), 6-0, and Kerber beat Renata Voracova 6-1, 6-1.
Top-seeded Caroline Wozniacki takes on Petra Martic on Tuesday.