PHILADELPHIA -- Philadelphia Phillies first baseman/designated hitter Bryce Harper left Thursday night's 6-2 win over the Washington Nationals with what the team called mid-back spasms.

Phillies manager Rob Thomson said afterward Harper will be day-to-day.

Harper was originally credited with an error on a Dominic Smith grounder in the fourth inning when he went to field a ball that hit the first base bag, then bounced off his chest. After reaching for the loose ball, television replays showed Harper trying to flex his legs and shoulders in an attempt to loosen his back. He stayed in the game before being pulled during the top of the fifth inning.

Harper was playing his 12th game at first base after starting as the Phillies designated hitter for 70 games following offseason Tommy John surgery that limited him to just eight games in right field in 2022. It's the first time he has moved to an infield position after 1,446 games as an outfielder or designated hitter.

For the season, Harper is hitting .293 with seven homers and 38 RBI. He was replaced at first base by Alec Bohm, who has received the majority of Philadelphia's starts at the position in place of the injured Rhys Hoskins, who was lost late in spring training with a left anterior cruciate ligament tear.

The Associated Press contributed to this report.