With Olympian L Devendro Singh (49 kg) getting a bye in his pre-quarterfinal match, half of the Indian team now stands a chance to make the final four of their respective weight divisions.
Commonwealth Games gold medallist Manoj Kumar (64 kg), National Games bronze medallist Mandeep Jangra (69 kg) and reigning National Champion Sukhdeep Singh (75 kg) had qualified for the last-eight yesterday.
Thapa (56kg), gold medal winner at the 2012 Asian Olympic Qualifying tournament, came out all charged against Lin Yen, who was caught off guard against the young Indian.
In the next round, he will square off against Kazakhstan National Champion Kairat Yeraliyev.
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Earlier in the tournament, L Devendro, a bronze medallist at the Limassol Boxing Cup in Cyprus, secured his spot in the quarters by virtue of a bye. The 21-year-old will now face off against a young and upcoming Uzbek boxer Nodirjon Mirzakhmedov.
But, there was disappointment in store for the Indian boxers in other weight divisions.
His campaign at the Asian Championships came to an end with loss on a split decision.