Top seeded Peng Shuai, a hot favourite in a weak Pattaya field after making it to the last 16 at the Australian Open, went down 3-6, 6-2, 2-6 to Doi, the world number 104.
The unfancied left-hander stunned her Chinese rival by taking the first set 6-3. She stumbled in the second (2-6) but regained her composure in the third, relying on her first serve returns to see out the match with a final 6-2 set.
Zvonareva, who won back-to-back Pattaya titles in 2009 and 2010, moved into the third round with a hard fought 7-6, 6-3 win over eight seed Shuai Zhang of China.
The 30-year-old Russian is on something of a comeback trail, after injury and poor form saw her drop from a top-ten career high in 2010 to a current WTA ranking of 189th in the world.