Right-hander Doug Fister is 4-1 with a 3.19 ERA in his first season with the Nationals. (Alex Brandon/AP)

After a forgettable first outing, Doug Fister has fit right in at the end of the Nationals’ rotation.

The right-hander, who missed the first month of the season with a lat injury, has surrendered only eight earned runs in his past five starts — all games the Nationals won.

And it hasn’t just been his fastball that’s been working for Fister. In his most recent start against the Phillies, he worked his curveball for a few strikeouts, and his changeup kept hitters off-balance.

“The main focus is staying down in the zone and being able to move in and out,” Fister said.

When searching for a pitcher to round out the rotation in 2013, the Nationals turned to Dan Haren. But that acquisition didn’t work out, with Haren going 10-14 with a 4.67 ERA.

This year, the Nationals replaced Haren with Fister and are reaping the benefits of the trade with Detroit.

In six starts this season, Fister (4-1, 3.19 ERA) has walked only 1.4 percent of the batters he’s faced, according to fangraphs.com. His WHIP is 0.982 and he’s struck out 28 batters in 36 2⁄3 innings.

“He’s awesome, isn’t he?” right fielder Jayson Werth said. “You gotta love playing behind a guy like that. He’s into the game. He works fast. He throws strikes. There’s not a whole lot there you don’t like.”

Fister has also shown his athleticism in the field. In the series finale against Philadelphia, Ryan Howard hit a ground ball to first baseman Adam LaRoche, who then attempted a double play by throwing the ball to Danny Espinosa, who was covering second base. Fister covered first and did his best to try to catch Espinosa’s throw before Howard could reach base. He extended his leg as far as possible before he was in a full split.

“I thought he blew out,” LaRoche said.

He didn’t. Fister got up and walked back to the mound to finish the inning.

The 6-foot-8 righty will be on the mound Tuesday against the NL-leading Giants. Prior to Monday’s game, the Nationals had won seven of their past 10 games.

“Playing together and well adds a lot of momentum to us,” Fister said. “We’re able to come in every day and put forth the energy, the focus and drive to play this game.”