Day nine of the Summer Olympics in Beijing, featuring swimmer Michael Phelps' historic gold-medal triumph, gave NBC its most watched Saturday prime-time broadcast in 18 years, the network said on Sunday.

The telecast averaged 31.1 million US viewers, NBC's biggest audience for a Saturday night program since an episode of "The Golden Girls" spinoff "Empty Nest" drew 31.4 million viewers in February 1990, according to Nielsen Media Research data cited by the network.

Phelps was just 4 years old at the time, NBC said.