The 43-ranked Zahlavova Strycova has beaten seeded players in three consecutive matches.
Zahlavova Strycova, who had never beaten Wozniacki in three meetings, needed six match points to advance.
She will meet either 2011 champion Petra Kvitova or Peng Shuai in the quarterfinals.
Wozniacki saved two match points in the 10th game and three more in the 12th before the Czech player prevailed. Wozniacki, who was serving, hit the ball wide after a Zahlavova Strycova drop shot.