With one out in the top of the ninth inning, Mets third baseman David Wright blooped the ball to short right field. Harper, who had switched over from center field in the sixth, charged hard after the ball and dove for it, but was unsuccessful. After throwing the ball into the cutoff man, Harper went back down to the ground in apparent pain.
"When he dove for the ball, I thought he just knocked the wind out of himself," Washington manager Davey Johnson said. "That predominately was the case. He also has been nursing a kind of tender back. So we'll have to monitor him pretty close."
Johnson added that Harper had been receiving treatment, a previously unheard revelation. Harper, for his part, repeatedly insisted after the game that he was fine.
"[It was] kind of sore, I was just trying to take a minute," Harper said. "I'm good. I'm totally fine to play, and I won't be out of the lineup."
Later, Harper was asked when he initially hurt his back. He responded, "I didn't hurt it. I'm good. Don't worry about it, I feel great."
Harper finished the game 0-for-4 with two strikeouts, dropping his average to .276.