The last time NBC drew this many viewers on a Saturday night, Michael Phelps was 4 years old. Over the weekend, Phelps’ record eighth gold medal win helped push NBC to its best Saturday night since 1990.

The network averaged 31.1 million viewers, peaking with 39.9 million from 11 to 11:30 p.m., when Phelps swam in his final race of the Beijing Games, the men’s 4x100 medley relay.

That gave Phelps his 14th career gold medal and eighth of this Olympics, surpassing Mark Spitz for the single-Games record.

It marked the biggest Saturday for NBC since “Empty Nest,” the “Golden Girls” spinoff, averaged 31.4 million viewers in 1990, and it was up 38 percent over the comparable night in Athens in 2004, which averaged 22.5 million.

It also gave the network a big kick heading into the final week of the Games. Though viewership traditionally drops in week two, with gymnastics and swimming, the two most popular events, now all but over, NBC still seems likely to record its best non-U.S. Summer Olympics numbers since Barcelona 1992.

Through nine days, the Games are averaging 30.1 million total viewers, 15 percent ahead of 26.2 million for Athens in 2004. The network is averaging a 17.4 household rating and 30 share, 10 percent better than a 15.8/28 for Athens and well ahead of what NBC had guaranteed advertisers.

In fact, late last week NBC sold off a chunk of inventory that had been reserved for makegoods, showing just how well the Games have gone thus far.

Saturday night proved once again that Phelps is the star of these Games. Some 70 million viewers tuned in for a portion of NBC’s primetime coverage.

The network averaged a 17.6/32 in households Saturday, up 29 percent over the same night in Athens four years ago.

Not surprisingly, NBC has been doing all it can to draw Phelps’ fans into its coverage now that his gold medal quest is over. Last night the network aired a heavily promoted extended interview with Phelps, his coach and his mom during the 8 p.m. hour.

It also produced a retrospective feature by Jimmy Roberts on Phelps’ feat and has advertised a Phelps DVD for sale on its NBCOlympics.com site.

Through nine days, NBC Universal has now drawn 191 million cumulative viewers to its Olympic coverage, including all who have watched for at least six minutes of coverage. That’s 14 million more than Athens and 5 million better than the 1996 Atlanta Games.

Beijing has now surpassed the total 17-day viewership for the Salt Lake City 2002 Winter Games and the 2000 Summer Games in Sydney.