Stefan Koubek of Austria knocked out former champion and seventh seed Paradorn Srichaphan to enter the quarter-finals of the Chennai Open.

He needed only 48 minutes to oust the struggling Thai, winning the second round match 6-1, 6-2, at the SDAT Nungambakkam stadium on Thursday.

Srichaphan, who had withdrawn from the Doha Asian Games singles due to a wrist injury, took a five-minute injury break to nurse his wrist and was completely off-colour.

The left-handed Koubek imparted heavy spin on his serves and made the Thai err by keeping the balls deep and heavy. He attacked Srichaphan's weak backhand.

Koubek, who upset Mario Ancic at the Mumbai ATP in September, said he was happy to come back to India and make it to the last eight.

"After I played the semi-final in Mumbai I thought I'd come here," said the Austrian after the match.