BEIJING— Zou Shiming has won China's first gold medal in boxing after Mongolian light flyweight Serdamba Purevdorj retired early in the second round of their title bout with an apparent shoulder injury.

The victory earned the host nation its 50th gold medal of the games.

Zou had a 1-0 lead after a tentative first round Sunday, but the Mongolian coach literally threw in the towel just 19 seconds into the second. Purevdorj had been fighting with his right arm handing limply at his side, though he was able to throw some punches with it.

Zou's victory fulfills four years of high expectations for the two-time world champion, whose bronze medal in Athens was China's first in a sport long banned by Mao.