CINCINNATI -- The Nationals' bullpen, which ranked last in the National League with a 7.06 ERA through 57 games, was in need of a boost. Holding a red-hot Reds offense to only two hits over the final five innings on Saturday could give them that.

Gerardo Parra hit a three-run homer and Matt Adams added a solo shot off former Nationals pitcher Tanner Roark, and the bullpen made an early lead hold up in a 5-2 victory at Great American Ball Park.

• Box score

“They came in and got 15 big outs,” Nationals manager Dave Martinez said of his much-maligned ‘pen. “They did fantastic. They’re making their pitches and locating their pitches. It gives not just confidence for them, but for the entire team.”

Right-hander Tanner Rainey, who ironically was acquired for Roark in a December trade, earned his first career victory with 1 1/13 scoreless innings with three strikeouts against his former team.

“It definitely was a special moment,” Rainey said. “Did my best to keep us right where we were. There’s maybe more motivation, just being back and facing the guys I faced in previous years. I didn’t know I got the win until after the game. Getting the first win here, it is special.”

Sean Doolittle notched his 11th save in 13 opportunities.

Roark, who spent six seasons in D.C., got the best of his former teammates at the plate, driving in two runs, one on a sacrifice bunt and another on his first career home run in the fourth off Nats starter Erick Fedde.

“It was a weird day,” Fedde said. “I had a lot of people on base and some tough at-bats. To come out of the game with a lead was nice. ‘Pen really picked me up.”

Parra hit a 1-2 pitch from Roark into the right-field seats for a three-run home run in the second to put the Nationals ahead 3-0. It was his fourth home run this season.

The Reds had runners in scoring position in four of the first five innings, but the Nationals got them to hit into three double plays to end the threats, including a pair of inning-enders.

“The ground balls really came into play, and that saved me today,” Fedde said. “To stay away from the big innings.”

Adams, who had three homers in his career against Roark, crushed a 1-0 pitch to right field that went an estimated 428 feet according to Statcast for his sixth homer in the fourth, making the score 4-1.

The two homers allowed by Roark were a season-high and ended a streak of 36 2/3 innings without allowing a homer.

Fedde allowed two earned runs in four-plus innings, but it could have been worse had it not been for the double plays.

“That was the key of the game,” said Reds manager David Bell. “We had the runners on early and didn’t come up with the hits. He made the pitches, however you want to look at it. He was able to settle down a little bit. But we did have the opportunities.”

Brian Dozier’s eighth home run this season, a solo shot in the ninth, capped the scoring for the Nats. The bullpen did the rest.

Rainey who appeared in eight games for the Reds last season left an impression on his new manager.

“He’s going to be a good one,” Martinez said. “He has that look when he comes in from the bullpen that I like.”