Martic defeated the eighth-seeded American 6-2, 7-6 (5) on No. 3 Court at the All England Club on Saturday.
The 28-year-old Pegula had reached the quarterfinals at this year’s Australian Open and French Open. She made it to the third round at Wimbledon for the first time.
Martic, who is ranked 80th, has been to the fourth round twice before at Wimbledon. She will next face 17th-seeded Elena Rybakina for a place in the quarterfinals.