Bryce Harper’s back flared up Saturday morning, forcing him to be kept out of the lineup of the season’s 14th game after committing himself over the winter to strengthening his back.

Harper told Phillies manager Joe Girardi that he woke up Saturday with tightness in his lower back. The Phillies said Harper’s absence was precautionary and considered him to be “day to day.”

Girardi believed Harper injured his back Friday night sliding head first into second base. The Phillies will stress caution as Harper’s lower back troubled him enough last September that he could not throw a baseball.

“Once you have some back issues, you’re always a little bit concerned about it,” Girardi said on the team’s pregame radio show. “Hopefully, it is short-term.”

Harper arrived a day late to spring training in February as he stayed in Las Vegas to finish a training program intended to keep his back healthy. Strengthening his back was an offseason priority.

Harper took six weeks off after the end of last season to rest his back and then worked five days a week with a personal trainer. He re-taught himself how to throw from the outfield, believing his throwing motion was ailing his back.

“I didn’t want to feel pain anymore,” Harper said at the start of spring training. “... I’m really looking forward to what we have going on, staying healthy, and continuing to stay healthy for the whole year.”

He was replaced Saturday in right field by Matt Joyce. Harper went 1-for-3 on Friday night but flew out twice to the warning track. He hit three balls harder than 103 mph as the winds in South Philadelphia prevented him from homering.

“I came to the Bank to hit homers and it’s just not happening,” Harper said after Friday’s 9-2 win. “That wind is brutal. I feel good. I have felt good in the box. It’s just getting pitches over the plate to do damage with and then take my walks. I really liked my last at-bat actually, some close pitches there that I didn’t swing at. I need to get back into that rhythm of taking pitches, hitting the ones over the plate.

“These last couple series I know I could have walked 10 to 11 times easily, but I just wasn’t doing that. I need to get back into that, doing damage over the plate and having better at-bats, seeing pitches, and getting on base by walking and not just by hits all the time.”

Harper first felt discomfort in his back last August, but played through the pain.

“I think you guys know how I am,” Harper said in February. “I don’t want to complain about anything that I go through. If it’s that bad then I’ll stop playing.”

The injury did not become public until Sept. 20 when Harper removed himself from a game. He was able to stay in the lineup down the stretch as the designated hitter, which he played for the team’s final four games.

“I told him, ‘Look, let’s get this right. Let’s not try to fight through this because we have such a long season. Last season was a sprint. This season is a marathon and we want you feeling good when you’re out there,’” Girardi said.

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Extra bases

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