The actor's rental bow tie had fallen off on his way to the ceremony, but producers Irwin Winkler and Robert Chartoff still dragged Mr. Stallone up to the stage. The fledgling actor might have been caught unprepared for the occasion, but he wasn't alone - most of Hollywood was surprised, too.
In fitting underdog fashion, Rocky upset a legendary class of films. Also up for best picture at the 1977 Oscars were three movies generally considered among the best America has produced: All the President's Men, Network and Taxi Driver. (Hal Ashby's Woody Guthrie biopic Bound for Glory was the fifth nomination.)
As the 30th anniversary of those Oscars nears, there are a few notable parallels. Mr. Stallone has again produced a Rocky film (Rocky Balboa), though it would have been fortunate to win one nomination, let alone the 10 that the original did. Taxi Driver director Martin Scorsese is again in the hunt with The Departed.
For many, however, the 49th Academy Awards remains exhibit A in any argument about the academy's less-than-perfect taste - a critique that usually cites the best-picture loss of Citizen Kane in 1942 (to John Ford's How Green Was My Valley), Alfred Hitchcock's lack of a best-director award, or Art Carney's best-actor win in 1975 over Mr. Nicholson (Chinatown), Al Pacino (The Godfather: Part II) and Dustin Hoffman (Lenny).
"In hindsight, it looks crazy that, of those nominated films, Rocky won - because Rocky is the flimsiest by far, and was so at the time," says film critic and historian David Thomson. "But at the time, there was this stupid notion that Sly Stallone represented a great American success story.
"It's a shining example of how silly (the Oscars) can be."
Rocky has almost certainly affected American culture more than the other three nominees - there is a statue of the film's main character in Philadelphia, after all. Propelled by Mr. Stallone's passion for it, the movie opened in limited release in late November of 1976 with modest hopes.
"It just kind of got momentum as it went along," Mr. Winkler says.
It won the Golden Globe for best drama and eventually landed two Oscars besides best picture: best director (John G. Avildsen) and best film editing.
All the President's Men, Network and Taxi Driver are all considered gems from one of the most vibrant periods of American cinema: the 1970s. It was then that directors - newly labeled as "auteurs" - such as Mr. Scorsese, Francis Ford Coppola and Robert Altman flourished.
When these films opened in 1976, it was the bicentennial, which many think affected the Oscar voting. Rocky was wrapped up in the flag - the boxer literally drapes it over himself in the movie's finale: a bicentennial bout against Apollo Creed.
"I think there was a kind of feeling in the country at the time - we had just gone through a decade of terrible social problems in America," remembers Mr. Winkler, who went on to produce films including Raging Bull, The Right Stuff and Goodfellas.
"And all of a sudden this movie came along and said, 'You know, if you believe in yourself, you'll be OK.' And suddenly it became part of what America was about. I think maybe if the picture had come out two years later or two years earlier, it might not have caught on the way it did," Mr. Winkler says.
Some would say, though, that Taxi Driver, Network and All the President's Men all said more about America than Rocky.
All the President's Men, which was nominated for eight Oscars and won four, depicted in step-by-step detail the reporting of Bob Woodward (Robert Redford) and Carl Bernstein (Mr. Hoffman) that exposed the depth of President Nixon's Watergate scandal.
Despite the questionable victory by Rocky, 1976 remains an impressive class for American films, which most years - 2006 included - would have difficulty living up to.
"We don't have those kind of pictures anymore," Mr. Thomson says. "We don't have the big entertainment that deals with serious subjects.
"Today, Network would be an independent film."