LOS ANGELES (Reuters) - A record 40.7 million Americans watched NBC television's coverage of the 2012 Olympics opening ceremony, making it the most-watched Summer Games opening, NBC said on Saturday.

NBC said the audience for the London ceremony was six million more than for the opening ceremonies from Beijing in 2008, and also beat the 39.8 million audience for the Atlanta Olympic Games in 1996.

U.S. viewers had to wait up to seven hours on Friday to watch the London ceremony after NBC decided not to stream it live and to delay its broadcast until the prime time evening hours.

NBC sports group chairman Mark Lazarus said in a statement on Saturday that the record audience for London "is a great early sign that our strategy of driving people to watch NBC in primetime is working."

NBCUniversal paid $1.18 billion for the U.S. rights to the London Olympics. It is streaming all the sporting events live online and boosting its TV coverage of the 2012 games to more than 5,500 hours.

But Americans took to Twitter in droves on Friday when they realized that the opening ceremony could not be seen until hours after it finished in the British capital.

CNN talk show host Piers Morgan, who was tweeting details about the ceremony from London, said on Friday: "Laughable that America is yet to start watching the Olympic ceremony on TV. Seriously."

NBC sports spokesman Christopher McCloskey said the opening ceremonies "are complex entertainment spectacles that do not translate well online because they require context, which our award-winning production team will provide for the large prime-time audiences that gather together to watch them."

In a decision that caused controversy in Britain, NBC cut a musical tribute from the opening ceremony for the victims of the July 2005 extremist attacks in London buses and trains. Instead the network showed a brief interview with Olympic champion swimmer Michael Phelps by "American Idol" host Ryan Seacrest.

NBC did not immediately return calls for comment on the matter.

(Reporting By Jill Serjeant; Editing by Vicki Allen)