Kvitova, last year’s Wimbledon runner-up, easily defeated American Nicole Gibbs, 6-2, 6-4, to advance to Thursday’s quarters.
She will next face eighth-seeded Czech Lucie Safarova, who crushed China’s Zheng Jie, 6-4, 6-0.
Former world number one Wozniacki, who is seeded third and seeking her fifth straight title at the event, improved to 19-0 lifetime in New Haven with a 7-6 (7/4), 6-2 victory over Sweden’s Sofia Arvidsson.
The hardcourt tournament, at the Connecticut Tennis Center at Yale University, is serving as a tune-up event for next week’s US Open.
Denmark’s Wozniacki defeated Czech Petra Cetkovska in last year's New Haven final.