Thailand hope to end their FIVB world championship campaign on a winning note when they take on Turkey in the final Pool F match on Thursday.
The injury-hit team have yet to pick up a win in the second round and on Wednesday suffered their third straight loss, against Bulgaria, following their defeats against China and Italy.
Thailand, who dropped to a 3-5 record, failed to convert a match point during the tie-breaking fifth-set as Bulgaria (3-5) won a 3-2 (25-18, 22-25, 18-25, 25-22, 19-17) thriller in just over two hours at the Osaka Municipal Central Gymnasium.
Onuma Sittirak scored 24 for Thailand while captain Pleumjit Thinkaow added 18.
Bulgaria's Nasya Dimitrova led all scorers with 28 points, with 22 spikes and five blocks, and Gergana Dimitrova had 20 points.
Having been already out of contention for a place in the final six, coach Danai Sriwacharamaytakul knew his players need to pull off something extraordinary today to win in order to finish the championship above the Turks in the standings.
"Our team numbers are limited but tomorrow is our last game and we hope to end with a win," said Danai.
"Today's game was really difficult because Bulgaria have good speed and a strong attack. In the first set we could not cope with Bulgaria's game plan especially their serve and block but in the second and third sets we reacted well to that."
"It was a tough game because Bulgaria have good speed and technique compared to other European teams," added captain Pleumjit.
"We could not play our game. It was unfortunate that we lost a lot of points in a row due to their strong serve. We have a limited number of players because of injuries but in training we have been trying different positions just in case we need to cover this, so our training has been good from this aspect," she added.
Meanwhile China handed defending world champions United States their first loss of the tournament and secured their place in the final six alongside unbeaten Italy.
China (7-1), who won 25-17, 26-24, 25-18, are second in the standings with 21 points while the Americans (7-1) are third with 19. Russia (6-2), who lost to unbeaten Italy (8-0) 22-25, 25-20, 25-18, 25-22 earlier in the day, are fourth on 18.
In the other game in the pool, Turkey defeated Azerbaijan 3-1 (26-24, 25-17, 22-25, 25-21) to improve to 4-4.
United States, who take on unbeaten Italy on Thursday, and Russia, who face China, will fight for the last remaining spot from Pool F on Thursday.