Taylor, 65, got as far as "Oh, beautiful" -- the first words of lyricist Katharine Lee Bates and composer Samuel Augustus Ward's 19th century song -- before he recovered and began singing the national anthem, prior to Thursday's game.
He later performed "America the Beautiful" during the seventh inning stretch.
Fox News reported some Twitter users poked fun at Taylor's error behind home plate at Fenway Park.
"I've seen fire and I've seen rain and at least I know which song is the #nationalanthem," one user said. Another tweaked, "James Taylor is great and all, but he just made up his own National Anthem."
"So what if James Taylor messed up? It was still beautiful," a Taylor defender chipped in.
Taylor led the stadium in singing "America the Beautiful," with survivors of the Boston Marathon bombing attack on the field, during the seventh inning stretch.
The St. Louis Cardinals beat the Boston Red Sox 4-2, to even the World Series 1-1. Game 3 is scheduled for Saturday in St. Louis.