Nationals starting pitcher Dan Haren needed only 90 pitches, 62 for strikes, to get through eight innings against the Atlanta Braves. (John Bazemore/AP)

In his first month as a Washington National, Dan Haren, the right-hander the team signed to a $13 million one-year deal to shore up the back of the rotation, was nothing short of underwhelming. One of the most effective starters of the previous decade, Haren, 32, only offered fleeting glimpses of the pitcher the Nationals thought they had signed.

On Thursday night, they finally saw the pitcher they pursued this winter, the efficient ace of the previous decade. Haren, 32, powered the Nationals to a 3-1 win over the Braves, helping them salvage a split in this four-game series and pushing their record back above .500.

Haren needed only 90 pitches, 62 for strikes, to get through eight innings, his longest outing since May 24 of last season with the Angels. He sat at 50 pitches through five innings, and his efficiency surprised even him. Haren walked only one batter and struck out four. In Haren’s last start, he allowed two runs over six innings, another step toward regaining his form. Thursday was a leap.

Entering Thursday’s game, Haren was among the least efficient pitchers in the majors with 16.8 pitches per inning and nearly 42 / 3 innings per outing. Against the Braves, it was like he was tossing batting practice; the Braves swung early and often, and when they made contact, the outs were routine. He averaged just 11.3 pitches per inning.

Haren’s lone mistake came on his 67th pitch, with two out in the sixth inning, a solo home run by Dan Uggla. The run snapped the Nationals’ streak of scoreless innings at 182 / 3 innings. Steve Lombardozzi singled to score Denard Span before Braves starter Kris Medlen (1-4) had retired a hitter, and Span drove in two more in the second inning with a double, giving Haren (3-3) all the support he would need. Rafael Soriano pitched an uneventful ninth for his ninth save.

The start from Haren came on the heels of Jordan Zimmermann’s eight scoreless innings Wednesday night. While the Nationals have yet to find a consistent groove a month into the season, the pitching performances of both starters alleviated frustration after two humbling losses start this series.

“We needed this game,” Haren said. “We needed it bad. And we needed yesterday and Jordan stepped up, so I wanted to do my part.”

Haren fooled the Braves offense with his array of pitches and aggressive approach. He had five innings of 12 pitches or less. Catcher Wilson Ramos noticed that the Braves swung early at first pitch and called for Haren’s trademark cutter instead of the typical fastball. “The first pitch of an at-bat, I’d treat it like an 0-2 pitch,” Haren said.

With movement, location and scouting, Haren worked through eight innings rarely throwing harder than 90 miles per hour. When he struggled earlier this season, he was trying to blend in with the rest of the hard-throwing rotation.

“I was trying to be too much like them,” he said. “I was overthrowing a little bit. I had a little bit of velocity back with my fastball, but I’m not gonna care about velocity anymore. I’m sick of that. It just gives me problems, so I’m just gonna be myself out there, whether it’s 88 or 85, I don’t really care. I know I can get people out. I challenge hitters and I can spot up, down and away, in, wherever.”

Haren allowed back-to-back two-out singles to Freddie Freeman and Evan Gattis in the fourth inning, the first hits allowed by the team’s pitching staff in 10 innings. A fielder’s choice groundout to Ian Desmond ended the inning.

Haren allowed his fourth hit with one out in the eighth inning, a hard pinch-hit single to center field by Reed Johnson. Jordan Schafer flew out to Span, another well-struck ball. Nationals Manager Davey Johnson emerged from the dugout to talk to Haren. Johnson had Drew Storen warming in the bullpen.

The Post’s Jonathan Forsythe says we should be worried about Stephen Strasburg’s pitching arm after his start on Monday night. (Post Sports Live)

The infield converged on the mound and Johnson, smiling, asked Haren how he felt. Haren told Johnson he felt fine and wanted to face Chris Johnson. Johnson rarely walks away the mound without having taken the ball from a pitcher. Once he heard Haren’s answer, he turned around and walked back.

“When we got to the ninth inning, I was fine with Soriano taking it,” Haren said. “But I wanted that guy.”

With four more pitches, Haren struck out Chris Johnson and high-fived teammates as he walked into the dugout.

Haren was staked to an almost instant lead to start the game. Span doubled to right field on the fifth pitch he saw. Medlen then uncorked a wild pitch that allowed Span to dash to third. Lombardozzi then snapped an 0-for-17 streak with a single to left for a 1-0 lead.

Span was the catalyst again an inning later. He slapped a ball down the third base line, playable by third baseman Johnson. The ball, however, sputtered past him. Both rookie Anthony Rendon, in his final game before returning to the minors Friday, and Ramos scored. The play was first ruled a two-run error but a few innings later amended to a two-run single. Span, acquired in an offseason trade to hit atop the Nationals lineup and patrol center field, now has 11 RBI, one more than middle of the order hitters Jayson Werth and Desmond. Werth exited the game in the fifth inning when his right hamstring tightened up again and is expected to miss a couple of games.

With a 3-0 lead, Haren didn’t let up. In vintage form, he continued to mow through the Atlanta lineup, efficiently looking like the pitcher they pursued this winter. And, Haren has grown comfortable again with his new team and what he can offer.

“That’s what he’s capable of doing,” Span said. “That’s the three-time All-Star Dan Haren right there.”