The Thai, who withdrew from last week's Fed Cup tie against the Slovak Republic to concentrate on her professional tour commitments, rallied from a set down to upset the 149th-ranked Castellvi 1-6 6-3 7-6 (7-4) in the first round.

"I couldn't adjust to her game and keep the balls in play in the first set. Then she seemed to have relaxed a bit and I just grabbed the opportunity. I went for my shots and the balls went in," said Napaporn, who plays Sarah Coles of Great Britain in the second round.

"I have never heard of her but I think she should be good. I'll just go out there and give it my best shot."

Meanwhile, two Thai players Nudnida Luangnam and Wilawan Choptang, made it to the quarter-finals in the $10,000 PTT Bangkok ITF Women's Circuit at Rama Gardens Hotel yesterday.

Top seed Nudnida edged out Uzbekistan's Vlada Ekshibarova 6-4 7-(7-5) in a thrilling second-round match. Compatriot Wilawan scored a convincing victory over countrywoman Nicha Lertpitaksinchai 6-1 6-1 in another match.

But Nungnadda Wannasuk and Pichittra Thongdach failed to emulate the two compatriots. Rising star Nungnadda went down to Ayu-Fani Damayanti of Indonesia 6-4 6-4, while Pichittra retired because of a knee injury while trailing Mauritius' Marinne Giraud 4-6 6-4 4-3.