The top-seeded Zvonareva handled Thai qualifier Varatchaya Wongteanchai 6-2, 7-5 on the hardcourts at Dusit Resort Pattaya. The Russian Zvonareva captured back-to-back titles in Pattaya City in 2009 and 2010.
The third-seeded Hantuchova resumed her winning ways at this event with a 6-2, 6-0 pasting of Thai wild card Nungnadda Wannasuk. Hantuchova beat Italian Sara Errani in last year's finale here.
Hantuchova will meet Pole Urszula Radwanska in the round of 16.
Other upsets came when qualifier Su-Wei Hsieh of Taipei humbled fifth-seeded Chinese Zheng Jie 6-3, 6-2 and Thai veteran Tamarine Tanasugarn took out sixth-seeded Kazakhstani Galina Voskoboeva, who retired while trailing 6-3, 4-2 due to a viral illness. The 34-year-old Tanasugarn was the Pattaya Open runner-up to Zvonareva two years ago and was also a finalist here way back in 1996.
Eighth-seeded American Vania King avoided the upset bug with a 6-4, 6-2 decision against Brit Heather Watson.
Additional first-round wins came for Amanmuradova, Radwanska, Russian Alla Kudryavtseva, qualifier Kai-Chen Chang of Taipei, Japan's Misaki Doi and 41- year-old Kimiko Date-Krumm, and Indian Sania Mirza, who titled here in 2009 and topped Japan's Ayumi Morita 3-6, 6-1, 6-2 on Tuesday.
The 2012 Pattaya City champion will collect $37,000.