The fourth-seeded Dementieva notched three aces and won six-of-seven break points in a relatively easy match against 19th-seeded Rezai.
Dementieva will face fifth-seeded Agnieszka Radwanska of Poland. Radwanska dispatched Marion Bartoli of France 6-3, 6-2 in 1 hour, 38 minutes.
Defending champion Vera Zvonareva of Russia fell to Samantha Stosur 6-2, 7-5. China's Zheng Jie advanced with a marathon win over Aussie Alicia Molik 6-3, 4-6, 7-6 (7-1).