Dementieva, last year's runner-up to Amelie Mauresmo, broke Pavlyuchenkova's serve five times and overcame four double faults of her own. She next plays either fifth-seeded Aravane Rezai of France or Andrea Petkovic of Germany.
Garbin got the better of the eighth-seeded Elena Vesnina of Russia 6-4, 2-6, 6-2 and will face either the second-seeded Flavia Pennetta of Italy or Alisa Kleybanova of Russia in the last eight. They were playing their second round match later Wednesday.
In Wednesday's remaining first round matches, Croatian wild card Petra Martic upset the third-seeded Yanina Wickmayer of Belgium 6-4, 3-6, 7-5, and Rezai defeated Evgeniya Rodina of Russia 6-4, 6-4.
Martic broke twice and dropped serve once. She will now play Hungary's Agnes Szavay. Wickmayer served 12 aces.
Oudin advances to 2nd round in ParisCopa del Rey round-up
