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The former world number four looked to be cruising to victory when she wrapped up the first set in just 21 minutes.

However her Thai opponent found her rhythm in the second set and Maleeva had no answer to her powerful strokes.

"The first set was just about perfect but she's a very good player on grass," said Maleeva.

"It's not a setback for me. I felt much better and my timing is a bit better. I have another 10 days to practice on grass before Wimbledon."

Tanasugarn, who is still suffering with a knee injury sustained in the French Open, will now play number nine seed Emilie Loit for a place in the semi-finals after her 6-4 7-6 win over Akiko Morigami.

"I wasn't aggressive in the first set and I started to realise I had to make her do something," said Tanasugarn.

Maria Sharapova has also made it into the last eight with a 6-4 6-3 victory over qualifier Samantha Stosur.

Sharapova, one of only four seeds left in the pre-Wimbledon grass-court tournament, did not quite have things all her own way and was broken as she served for the match at 5-2 in the second set.

But she broke back immediately and now faces another Australian Alicia Molik in the quarter-finals.