From the Los Angeles Times:
Williams said he never tired of singing "Moon River," whose melody he considered "beautiful" and whose lyrics he called "timeless."
"You wouldn't believe how 'Moon River' became a hit," he said in a 1989 interview with the Chicago Tribune. "I was having dinner with [songwriters] Henry Mancini and Johnny Mercer, who had just finished recording the movie Breakfast at Tiffany's, with Audrey Hepburn singing 'Moon River' out on the balcony with a guitar.
"So Mancini and Mercer played this song for me, which I thought was great. But my record company was really into singles then, and they said: 'I don't think phrases like 'my Huckleberry friend' will make it with the kids — they won't know what it means.'"
But about four weeks before the 1962 Academy Awards program, he recalled, "I was invited to sing 'Moon River' on the Oscars show, and Columbia Records decided we ought to rush a 'Moon River' album into the stores, because that tune looked like a shoo-in for the 'best song' Oscar.
"So they quickly put out an album, had it in the stores on the day of the Oscars, and the next morning it sold 500,000 copies."