It was his first game of the 2014 season for the A's, who beat the Miami Marlins, 4-3, thanks to Freiman's shot.
Freiman, 27, made his professional debut last year but has spent most of this season playing Triple A ball.
He said he was thrilled to get the callup Sunday.
"I was wired," he told the San Francisco Chronicle. "I drank a lot of coffee."Freiman was called up after Josh Reddick, a former member of the Boston Red Sox, hurt his knee.
Freiman, who stands a towering 6 feet, 8 inches, played baseball at Wellesley High School. He played 80 games for the A's last year and was named the Rookie of the Month in May.
The A's were scheduled to play the Detroit Tigers Monday night. It was unclear if Freiman will be in the lineup.