San Diego‘s Kyle Blanks, right, rounds the bases after a two-run homer in the fifth inning off Dan Haren. (Lenny Ignelzi/Associated Press)

At times during their first week out West, the Washington Nationals showed glimpses of shedding their disappointing start to this season. At times during Sunday afternoon’s 13-4 dismantling at the hands of the San Diego Padres, they played as if intent on reversing any positive thrust they had gathered. The Nationals’ offense showed a pulse, at least, but only after starter Dan Haren tumbled back into his troubling, early-season form and before their bullpen imploded.

After Haren’s worst start in nearly a month, an afternoon of pitches left high in the zone and rockets flying off the Padres’ bats, the Nationals departed Petco Park 3-4 so far on a 10-day road swing, another rough spot in a season still sitting on the runway. The season is more than a quarter old, June arrives in less than two weeks and the Nationals, predicted to dominate, injuries or not, will head into San Francisco on Monday with a 23-21 record.

“We’ve just kind of been hovering around .500, win a few, lose a few,” Haren said. “We’re not healthy. That’s one thing. We haven’t hit our stride yet, but I’m sure it’s coming. We have too much talent to be playing this mediocre.”

The Nationals had won twice in a row leading into Saturday evening, and the next two days they responded with five runs and two losses. Injury has played a role. After he ran into a wall in Los Angeles, Bryce Harper has been out of the lineup four times, missing the last two games in San Diego. Harper continues to receive extensive treatment on a swollen left knee, Manager Davey Johnson said, and his status for the series opener in San Francisco will be determined Monday.

“We just need to get everyone healthy,” third baseman Ryan Zimmerman said. “I don’t know if Bryce is going to be able to play or what’s going on with that.”

Adding to Harper’s absence, Jayson Werth has been on the disabled list since May 3. Their subs, so good last year, have mostly slumped and the Nationals’ lineup has stalled outside the middle. Adam LaRoche and Zimmerman have driven in 19 runs this road trip; all other Nationals hitters have driven in five.

“You have to have a lot of patience sometimes in this job,” Johnson said. “The middle of the lineup is swinging the bat very good. Other guys, it looks like they’re starting to come around. I like the way the pitching has been. Sometimes, it just takes time to jell.”

Starts and stops have defined the Nationals’ first two months, and few represent that better than Haren, the primary culprit Sunday afternoon.

Haren had accumulated momentum over his previous four starts, winning three games and pitching well enough to win Tuesday in Los Angeles. The Padres shelled him, recalling the first four starts of Haren’s Washington tenure, which had left his ERA at 7.36. He allowed seven runs in five innings on nine hits, few of them cheap, and two walks.

“I’m definitely disappointed,” Haren said. “My confidence was high. But baseball is a very humbling game. It will bring you down when you feel up. The best thing to do is just try to forget about it, as hard as it is. Just move on to the next one. I’ve been throwing the ball well. I’ve been having a good feeling about how things are going out there. I kind of put aside the struggles of the first few weeks of the season. I can’t let it bring me down. I got to give us a chance next time.”

After he narrowly lost a duel with Clayton Kershaw in his last start, Haren wheezed from the start. He felt fine physically, but mechanically, “something was off,” Haren said. “I just wasn’t myself today.” Everth Cabrera roped a single into center to lead off the bottom of the first. A walk and doubles from Carlos Quentin and Jedd Gyorko gave the Padres a 3-0 lead before the inning ended.

The inning set the theme for Haren’s demise: cutters and splitters thrown with little tilt, left up in the strike zone. At this stage of his career, Haren, 32, operates with a narrow margin for error; he can still baffle lineups when his mid-80s collection of darting and sinking pitches find the corners. When he leaves them over the plate and up, hitters treat it like batting practice.

“The ball was just up all day,” Haren said. “It doesn’t matter if you’re playing the Padres or Tigers. If you leave balls out over the plate and up, they’re going to hammer it. I made way too many mistakes. I wasn’t able to keep it close.”

Haren settled for three innings, and Zimmerman launched Andrew Cashner’s hanging, 3-1 change-up 414 feet, into the upper deck in left in the fourth. Steve Lombardozzi, on base after one of his three hits, also trotted home to make it 3-2.

The Nationals would not remain competitive much longer. Will Venable smashed a belt-high cutter over the right field-fence to lead off the bottom of the fifth. Yonder Alonso doubled, Gyorko singled and hulking Kyle Blanks made a baseball disappear, lining another hanging cutter off the Western Metal Supply Company sign, giving the Padres a 7-2 lead.

Johnson planned to let his regulars play only one more inning. Then the Nationals strung four straight singles together in the seventh, knocking out Cashner and inching back into a 7-4 game. As Denard Span came back into the dugout after crossing the plate, Johnson told him: “You’re staying in now. We’re about to win this game.”

These Nationals, though, are in no condition to stage galvanizing comebacks. In the last of the seventh, the Padres brutalized Ryan Mattheus for five runs in one inning. Alonso finalized the scoring in the eighth, crushing the first pitch from Drew Storen over the right field fence.

The Nationals may set aside mediocrity soon and play to the level their talent suggests. Maybe they will get healthy and recapture the vibes from 2012. Sunday, all they had was another lost afternoon, more fit than start.

“It’s real disappointing,” Johnson said. “I hate to even talk about that one today.”