Christopher gained the weight back and rejoined the Athletics for the 1947 season. While there was talk of keeping him in the rotation, he ended up becoming a full-time reliever for the team. Despite this, Christopher was still able to contribute with his bat; he drove in the winning run in a May 29 game against the Red Sox. Over the course of the season, Christopher evolved into the Athletics' closer, finishing the games when the team's pitchers could not go the distance. He finished the season having played 44 games, finishing 38 of them and getting 12 saves in the process. He also had 10 wins, seven losses, and a 2.90 ERA. At the end of the season, Christopher was holding out on his contract, wanting either a starting role in the rotation or more money to remain a reliever. The two sides agreed to a deal at the end of February, and he looked to be a starting pitcher during the 1948 season.