"With Billy Martin on third and two out, Mantle hit a towering 450-foot drive to center. The ball landed on the running track and bounced some 15 feet up into the centerfield bleachers for a ground-rule double."

It was a double, at least for a while. But it was changed to a single, in accordance with the scoring rules [since Martin was on third].
...
In my effort to verify my memory of the hit as a single, I encountered a few surprises. Ken Hirdt at Elias Sports Bureau, the official statistician of Major League Baseball, located the game and the precise date. His check of the official scorer's report showed a double and a single for Mantle, not two doubles.

Ken's info was confirmed by Dave Smith of Retrosheet. Dave sent me the game's play-by-play and photo copies of the Yankees and Orioles scorebooks. These proved that Mantle's first double came in the third inning, in which the Yankees failed to score. That meant his one RBI came on the ninth-inning hit and had to be a single. Also, the official play-by-play of that final inning said: "Mantle singled to centerfield and Martin scored."

The Yankees scorekeeper also noted in his ninth-inning entry that Mantle's hit "bounced once into cf bleachers."

There is no doubt the hit was a single. Yet, my fellow researchers and I have never been able to find a correction of the original story. In printed material, it is always a double.