If the Washington Nationals want to consider their deficit in the N.L. East, they need to look no further than the team across the diamond from them Sunday. The Atlanta Braves took advantage of the Nats bullpen yet again, while Washington could muster nothing against the Braves’, falling in the series finale 6-3. With the loss, the Nats drop below .500 (28-29).

The Braves lead in the East stretched to a whopping 6 1/2 games — the largest in baseball currently. The Nats have a season series record against the Braves of 3-7, accounting for a large portion of that deficit.

As was the case Saturday night, the Nats bullpen could not handle their responsibility, as Zach Duke walked four and gave up two hits in his two-thirds of an inning, effectively digging the Nats hitters a hole they are incapable of rallying from these days.

Duke’s incapacity to throw strikes Sunday made a loser out of Nathan Karns (0-1, 6.00). Karns was not as strong as in his debut, but left two runners on base when he left the game, and Duke allowed both to score. The rookie, who made his second MLB start, gave up four runs — three earned — on seven hits and a walk, striking out six in 4 2/3 innings.

After the Nats went in order in the top of the first against Braves starter Paul Maholm (W, 7-4, 3.68), the Braves jumped right on Karns. Leadoff hitter Andrelton Simmons reached on a throwing error by Ryan Zimmerman, his tenth of the season. The next hitter, Ramiro Pena, clobbered a fastball into the stands in right for an early 2-0 lead for Atlanta.

The Nats got both runs back in the second. Adam LaRoche doubled to lead off and went to third on Ian Desmond’s bunt single. Tyler Moore followed with a run-scoring single to left to get the Nats on the board. Later in the inning, Maholm butchered Karns’ popped up bunt. All hands were safe, and Desmond scooted home with the then-tying run.

The tie didn’t last long, as B.J. Upton homered off Karns in the bottom half of the inning to re-take the lead.

Things stayed that way until the fateful fifth inning. Justin Upton started the Braves rally with a one-out single off Karns. After the Nats righty got Freddie Freeman to fly out, he lost Evan Gattis on a 3-2 fastball after having the slugger down 0-2. Manager Davey Johnson called on Duke at that point, and Duke did nothing but pour gasoline on the fire. On Duke’s ninth pitch to Brian McCann, the Braves catcher finally got one he could handle, slapping a single to left field to plate Upton. Duke got out of the inning without more damage, but he wasn’t done yet.

Desmond homered in the top of the sixth to cut the Braves lead to 4-3. In the bottom of the frame, Duke walked the first two batters he faced. After a sacrifice bunt moved the runners up, Duke intentionally walked Justin Upton to face Freeman. The decision backfired, as Freeman doubled off the top of the wall in left field, plating two more runs. The play was reviewed as the Braves thought the hit was a home run, but the call on the field stood.

Not that it mattered.

The Nats went hitless in the last three innings, failing to muster any sort of comeback. Washington has yet to score on the Braves bullpen in their ten games this season. For the entire year, the Nats are hitting .194/.252/.286 in innings seven though nine.

THE GOOD: Right-hander Erik Davis, called up Saturday from Triple-A Syracuse, made a successful Major League debut, throwing 1 2/3 perfect innings of relief, recording two strikeouts.

THE BAD: The bottom third of the Nats order went 1-for-9 with five runners left stranded.

THE UGLY: Zach Duke. Whatever magic the lefty used last season to get his name back in good graces, he must have used all up. His ERA sits at 8.71 now and just continues to have poor performance after another, giving up multiple runs in four of his last five appearances.

THE STATS: 5 hits, 0 BBs, 4 Ks. 2-for-6 with RISP, 3 LOB. E: Zimmerman (10, throw). No DPs.

NEXT GAME: Tuesday at 7:05 against the New York Mets at Nationals Park. Jordan Zimmermann (8-3, 2.37) hosts Jeremy Hefner (1-5, 4.74).