Allen, the 2004 world amateur champion, was the favourite to win the match, but it was Passakorn, fresh from his victory in the Asian Under-21 Championship in Tehran in May, who was off the blocks first.

Passakorn, a 20-year-old from Nakhon Pathom province, took the first frame with relative ease and staged a big recovery to win the second on the black ball with a 57-point clearance at the Hua Hin Grand Hotel.

Allen then scored breaks of 62 and 83 to tie score at 2-2 and took the fifth despite a fine run of 64 points by Passakorn to go 3-2 up.

Passakorn, who showed a bit of nerves as Allen nudged ahead, regained his composure and captured two frames on the trot to end Allen's run in the tournament. Allen becomes the second wildcard to lose in the last 16 round after world No 27 Ding Junhui of China exited on Wednesday. Local snooker hero Ratchapol Pu-Ob-Orm, ranked No 25 in the world, scored another easy victory, defeating Surathep Phoochalam 4-1 in their last 16 round encounter.

Wattana, whose highest break in the match was a 65-point run in the second frame, said: "I am still finding it difficult to get my rhythm and I struggled a bit today. Lucky that Surathep was not up to it.

"The quarter-final tomorrow [Friday] against Passakorn could be a tougher battle, if my young friend doesn't lose his nerves. He is a very capable player and I am sure he will improve even further with time."

Today's quarter-final matches will start at 10am at the same venue.

Results

Wednesday's last 16 round: Atthasit Mahitthi beat Noppadon Noppachorn 4-0 (64-60, 77(57)-27, 78-37, 70(55)-34)

Yesterday's last 16 round: Passakorn Suwannawat beat Mark Allen (Northern Ireland) 4-3 (69-35, 77(53)-52(52), 7-119(62), 5-98(83) 78(64)-79, 66-25, 71-24); Ratchapol Pu-Ob-Orm beat Surathep Phoochalam 4-1 (65-15, 122(65)-16, 47-60, 60-34, 72-26); Wanchana Poomjaeng beat Karnchai Wongjan 4-1 (65-59, 23-62, 46-35, 63-15, 68-32)

Agencies

Hua Hin