The 21-year-old from Samut Sakorn defied a late fightback from Suchanan, ranked 192, to win the second-round match 6-2 3-6 7-6 (7-1), levelling their head-to-head record at 2-2 with her countrywoman.

"I was up 5-2 and had three match points in the final set but she came back to level at 5 all. I lifted my game and gave her little chance,'' said Monthinee, No 284 in the WTA rankings.

"I went for my shots whenever I got an opportunity. I didn't give her a lot of space because she is capable of hitting down-the-line winners,'' said Monthinee who is in her first quarter-finals of a Challenger event.

Awaiting her in the quarter-final will be eighth seed Napaporn Tongsalee, who regained her form after making seven first-round exits. Yesterday, she crawled her way back from a first-set deficit to beat Brazil's Larissa Carvalho 1-6 6-4 6-1.

 "She is a good player and she is getting her confidence back. It will be tough for me because I have an injury to my abdomen,'' said Monthinee, who edged out Napaporn 6-7 (4-7) 7-6 (7-2) 7-6 (7-5) in Minnesota in February.

Meanwhile top seed Tamarine Tanasugarn struggled to beat Czech Veronika Chvojkova 6-4 4-6 7-5 on way to the quarter-finals. She  will play China's Chen Yan-chong today.