Harper slipped on damp grass in the sixth inning making a throw Thursday night and gingerly walked off the field.
After he received medical treatment Friday and Saturday, Nationals manager Matt Williams put him back in right field for Saturday afternoon's game.
Williams had said he would "monitor" the 22-year-old two-time All-Star.
"If we see anything that tells us he is gimpy or not feeling well, then we'll get him out," Williams said. "But he wants to play. He feels good enough to play."
Harper has dealt with several lower-body injuries through his four-year career, most recently undergoing surgery on his left knee after the 2013 season. He also missed roughly a third of last season with a thumb injury.
"I've played through pain the past two years sometimes," Harper said. "It feels OK, but just trying to get in there and play for the team."
Harper's injury is the latest in a string for the Nationals.
Williams said starter Stephen Strasburg (neck tightness) might return to the team's rotation this week after he pitched a successful bullpen session Saturday.
Outfielder Jayson Werth is aiming for an Aug. 1 return from a left wrist injury that included bone fractures, and infielder Ryan Zimmerman went on the disabled list retroactive to June 10 with plantar fasciitis in his left foot.
The Associated Press contributed to this report.