NBC finished a hugely successful Olympics with another strong tune-in, airing the most-watched closing ceremonies for any non-U.S. Games since Montreal 1976.

Though ratings for Beijing fell off during the second week of competition, NBC still outpaced Athens 2004 by a sizeable margin in both total viewers and households and made its ratings guarantees to advertisers.

Sunday’s closing ceremonies averaged 27.2 million total viewers, up 39 percent over the 19.6 million who tuned in for Athens. Among households, NBC averaged a 15.2 rating and 24 share in primetime, 28 percent better than 2004’s 11.9/20.

The network undoubtedly got a boost from another appearance by Michael Phelps, the hero of these Games, who flew to London to help symbolically pass the torch for the 2012 Olympics. His cameo had been heavily promoted.

That brought to a close a dominant Olympic performance by NBC, which won all 100 half hours of Games broadcasts against the other broadcast networks, a feat it did not manage during the most recent Winter Games, Torino 2006.

The big numbers for the Games pumped up interest in the upcoming bidding for the 2016 Summer Games, with ABC, CBS and Fox all considering submitting proposals.

Most significantly, it proved there’s still room for major primetime events in this fractured, time-shifted TV viewing environment. While ratings for nearly every broadcast primetime show have plummeted over the past two years, sports have surged this year.

The Olympics set a record for most cumulative viewers, months after Fox broke the record for most Super Bowl viewers and ABC saw big ratings increases for its NBA finals.

More than 211 million viewers tuned in to some portion of the Games on NBC Universal, 2 million more than the old record holder, Atlanta. A final number for Beijing will be out later today.

NBC’s 17-day average primetime viewership was 27.7 million, 13 percent better than Athens’ 24.6 million and the best for any non-U.S. Olympics since Montreal 1976.

Among households, NBC averaged a 16.2 rating and 28 share, more than a point ahead of its guarantee to advertisers and up 8 percent over Athens’ 15.0/26. It was the best average for a non-U.S. Games since Barcelona 1992.

Beijing opened with huge numbers, scoring the highest-rated non-domestic opening ceremonies since Rome in 1960. Over the first week of competition, Phelps’ pursuit of a record eight gold medals and the strong U.S. women’s gymnastics teams kept audiences tuning in at very high levels.

NBC achieved its best Saturday night viewership in nearly two decades when Phelps swam live for his eighth gold. Though numbers for the Games dipped in week two, as they do in nearly every Olympics, Beijing managed to maintain its lead over Athens mostly due to that strong first week.

NBC has the rights to the 2012 London Games as well.