Michael Saunders slides into second base in the ninth inning, but Daniel Murphy is able to complete a double play for the Nationals. Tanner Roark pitched seven strong innings, but a patched together lineup wasn’t able to overcome a late homer run given up by Joe Blanton. (Jonathan Newton/The Washington Post)

When Bryce Harper gave up his frantic but fruitless pursuit of Cesar Hernandez’s flyball, Joe Blanton turned back to the pitcher’s mound and convulsed as he hollered into the afternoon air, helpless to do anything else after the decisive home run in the Washington Nationals4-2 loss to the Philadelphia Phillies flew out to right-center field on Saturday afternoon.

As evidenced by the relative ease with which Blanton retired the batters around Hernandez in the eighth inning, he does and should expect better. As evidenced by his frustration, the veteran has disappointed so far. Outside of the three scoreless innings he threw in relief of Jeremy Guthrie last week, Blanton has given up seven hits in four inning s — three of them home runs.

Saturday’s shot undid a strong performance from starter Tanner Roark and scuttled an afternoon on which it seemed the Nationals could steal a win while resting several regulars. It renewed concern about this Nationals bullpen, which looked steady Friday. And it left a 13-year veteran to answer questions about what went wrong again.

But Blanton had an answer to those questions: His mechanics are out of whack, and try as he might, he cannot get them back in-sync.

“I’m a touch off right now,” Blanton said. “The stuff doesn’t play the way it should. You don’t locate as well. Just trying to come back in the groove a little bit.”

Walks and home runs have plagued the bullpen through the opening part of the season. While Nationals starters have allowed two home runs in 11 game s, the shot Blanton allowed Saturday upped the bullpen’s total to 10. That he preceded that home run by hitting Freddy Galvis with a pitch made the whole thing a representative relief showing.

But for Blanton, the trouble has been that he is hanging his slider, a pitch that grows sharper with time and use. Saturday’s homer came against a fastball, one he left at the knees and over the middle of the plate — one he meant to throw up, in, and out of the strike zone. When his mechanics are off, his command suffers.

“It’s frustrating because you know why it’s happening,” Blanton said. “. . . But at the same time, there’s a positivity to it that it’s something you can fix instead of, ‘Wow, I feel good and I don’t know what’s happening.’ That’s a lost feeling, and I don’t have that right now.”

By the time he met with reporters an hour after the game, Blanton did not seem lost nor angry, but thoughtful and hopeful. His initial reaction on the field made sense, given that Hernandez’s home run came just after Chris Heisey had tied the game and taken Roark off the hook for what would have been a tough-luck loss.

Roark initially worked with a lead, as Anthony Rendon singled home a run in the third, his second two-out RBI in two games, giving him three times as many RBI this April (3) as he had last April (1). Rendon was one of five regulars in the lineup Saturday. Because the Nationals have a day off Monday, Manager Dusty Baker did not want to rest regulars Sunday, as is the usual, and leave hitters without an at-bat for two days. Such a layoff can interrupt rhythm.

So instead, he rested Matt Wieters, Adam Eaton and Jayson Werth, all of whom had played in every game this season; Wieters had started all but one. His replacement, Jose Lobaton, walked with one out in the third to start a rally. Then Roark provided the Nationals’ first hit against Phillies starter Jeremy Hellickson, a single through the right side, eventually setting up the Rendon single.

So Roark had a lead and momentum entering the fourth, when the first two Phillies bunted for hits and Odubel Herrera doubled. The Nationals trailed 2-1. An inning later, Galvis, who pummels the Nationals whenever he sees them, took a more literal approach and lined a ball off Roark’s throwing arm. Roark stayed in the game, doubled in his next at-bat, and finished seven innings having given up two runs on four hits .

Meanwhile, the Nationals continued to hit deep flyballs into the afternoon sun, un-affectionately known at Nationals Park as “the sun monster” to those who struggle to see through it during day games here. A few odd routes aside, the Phillies handled those flyballs well, leaving the Nationals with nothing more to show for their offensive efforts by the seventh inning. Then Heisey, getting his first start of the season, homered to tie the game.

“Today was atom-ball Saturday, because I’m telling you we hit some balls extremely hard that most of the time, I thought some of those balls were capable of leaving the park,” Baker said. “So we just have to go back to the drawing board and stay positive and stay confident — and keep Joe and the rest of our bullpen positive.”

Baker chose Blanton to pitch the eighth, and after he hit Galvis in the foot, Hernandez punished him with the two-run home run. Blanton allowed seven home runs each in 2015 and 2016. He is almost halfway there.

“Sometimes it’s about grinding through it. It’s a long season. Everybody has those bouts here and there,” Blanton said. “That’s mine right now.”

As has been the case in four of the Nationals’ five losses this year, the bullpen contributed to their demise once again. Like Blanton, that group does and should expect better. So far, it simply hasn’t pitched that way.