China remained unbeaten with a five-set victory over South Korea.
It was a typical match between the Asian rivals, with long rallies and endless defense. China won, 17-16, 16-14, 2-15, 13-15, 15-13. It was the first time this Olympics that a match required the fifth-set tiebreaker, in which points are scored on every serve.
Youngmei Wu scored the winning point on a stuff block.
The match lasted nearly three hours, and the crowd at the Omni gave both teams a standing ovation when it ended. China is 2-0 and South Korea 1-1.
Japan had an easier time in its Pool A match, sweeping the Ukraine, 15-9, 15-5, 15-4. Japan improved to 1-1 while the Ukraine fell to 0-2.
In Monday's late match, second-ranked Brazil upset defending Olympic champion Cuba, 15-11, 15-10, 15-4.
In other matches: Russia overwhelmed Canada, 15-1, 15-7, 15-9, and Germany beat Peru, 15-11, 15-6, 15-3.