Stephen Strasburg gives up an RBI single to Carlos Ruiz in the fourth inning. (Matt Slocum/Associated Press)

Tyler Clippard had just finished talking with shortstop Ian Desmond on the mound when Manager Davey Johnson emerged from the dugout. He was there to take the ball away from Clippard mid-inning, a rarity during the reliever’s dominant season on the mound. Clippard stumbled during the most important moment of the night Monday for the first time in what has felt like an eternity as the Washington Nationals fell, 3-2, to the Philadelphia Phillies.

Clippard has been the most reliable pitcher on the Nationals, so it’s hard to fault him. He was trusted with a high-pressure, late-game situation, a 2-1 lead in the eighth inning during a final-gasp push for the playoffs, and he buckled. He allowed two runs, capped by Carlos Ruiz’s go-ahead single and a Jimmy Rollins slide into home plate that just beat Bryce Harper’s throw and Wilson Ramos’s tag.

“It’s never easy, man,” said Clippard, who entered the game with a team-leading 1.94 ERA and hadn’t allowed a game-changing run since Aug. 5. “You could go 40 scoreless and give it up one night. It’s never easy. Losing sucks.”

The Nationals dropped to 71 / 2 games behind the Cincinnati Reds for the second wild-card spot. The Phillies had essentially gift-wrapped the game in the top of the eighth when starter Cole Hamels was removed after seven dominant innings despite a low pitch count. The Nationals capitalized against one of the worst bullpens in baseball, taking a 2-1 lead on a sacrifice fly by Scott Hairston with the bases loaded.

But oddly enough, it was the Nationals’ most trusted reliever — and one of the best setup men in baseball — who cost them the win.

“It’s a stab in the heart,” Johnson said. “We’ve got to win these games. We had opportunities. We didn’t capitalize on them.

After retiring the first two batters, Clippard walked rookie Cesar Hernandez. Clippard, who has held left-handed batters to a .148 average this season, then faced Rollins, who fouled off five pitches before drilling an RBI double to right that tied the score at 2.

Then came the final blow. After Chase Utley was intentionally walked, Ruiz smacked a single to shallow left. Harper — who hobbled all game with a limp because of a hip issue Johnson said he hadn’t been informed of — scooped up the ball and fired home. The throw was to the third base side of home plate. Ramos corralled it and dove to his right to tag Rollins. Rollins adjusted, and his slide barely beat the tag. Disappointed, Harper hunched over at the waist.

“That was close,” Ramos said. “If it was a throw a little bit more towards the plate, I get a chance to get that guy out.”

Harper has run gingerly at times over the past two days but has insisted to Johnson and coaches he is fine. The bruised knee that forced him to miss a month of the season hasn’t been an issue. Not until Monday did Johnson discover Harper has been receiving treatment on his hip.

“I was a little disturbed that I wasn’t informed,” Johnson said.

Harper wouldn’t address the hip issue following the game.

“I’m fine,” he said. “Just like I told him, if I was hurting, I’d come out of the game. I feel good.”

The Nationals put runners on the corners with one out in the ninth inning against Phillies closer Jonathon Papelbon thanks to singles by Desmond and Adam LaRoche. But back-to-back strikeouts by Ramos and Anthony Rendon squandered that opportunity. As he walked off the field, Ramos barked back at home plate umpire Jerry Meals for a called third strike that appeared to be just outside the strike zone but was framed by catcher Ruiz.

“Those pitches for me was balls,” Ramos said. “They call them strikes.”

“Obviously it was a pretty generous strike zone,” Johnson added. “Nobody got a lot of hits. He did call the low pitch all night. So I don’t have any complaints. He was just calling a pretty generous strike zone.”

For seven innings, Hamels and Stephen Strasburg were entangled in a pitchers’ duel. Hamels’s lone mistake was a solo home run surrendered to Ryan Zimmerman in the first inning. But locked in a 1-1 tie through seven innings, Phillies interim manager Ryne Sandberg pulled the plug on his dominant starter. Hamels had allowed only one run on two hits and thrown 87 pitches. Sandberg gave the ball to the Phillies’ bullpen, and the relievers instantly made a mess of Hamels’s gem.

The Nationals loaded the bases in the eighth inning on a single by Rendon and a walk by pinch-hitter Chad Tracy against right-hander Justin De Fratus and a five-pitch walk by Harper against left-hander Cesar Jimenez. Hairston, who had struck out in his previous three at-bats, delivered a flyball to shallow center field that scored Rendon. It could have been more.

“We could’ve broken the game open when Hairston was hitting,” Johnson said. “We’re just not getting it done.”

For his part, Strasburg was dominant for six innings, striking out 10 batters. He didn’t allow a hit until the fourth inning, but it came at an inopportune moment. He walked Rollins, and with Utley batting, Ramos tried to throw him out at first. Ramos’s throw smacked Utley’s bat on his follow-through. Rollins took off for second, and Ramos was charged with an error.

On a 2-2 fastball to the next batter, Rollins caught Strasburg not paying attention to him and broke for third. Rollins was nearly halfway to third when Ruiz made contact. The broken-bat single to center scored Rollins to tie the game at 1. Because he was sweating on a humid night, Strasburg struggled gripping the ball and locating his fastball and grew tired by the final inning. Johnson removed him and turned the ball over to the bullpen and Clippard.