The Washington Nationals were locked in another tight, low-scoring game when the most unusual thing happened: Their bullpen let the lead slip away.

Sean Burnett gave up two-run homer to Matt Wieters in the eighth inning, and the Nationals lost 2-1 to the Baltimore Orioles on Sunday in the deciding game of this tense interleague series.

Ryan Zimmerman, who received a cortisone shot in his sore right shoulder before the game, gave Washington a 1-0 lead with an RBI single in the third inning. The score stayed that way until the eighth, when the usually reliable Burnett yielded a leadoff single to Adam Jones before Wieters connected on an 0-1 pitch.

"I tried to go with my strength and left the ball out over the plate," Burnett said. "He's a good hitter and made me pay for it."

Burnett came in with a 1.04 ERA and had kept the opposition scoreless in 28 of 31 appearances. Washington dropped to 34-3 when leading after seven innings and 14-12 in one-run games.

"We play a lot of close games and our bullpen expects to get the job done in those situations," Burnett said. "Today I let one slip away."

Each team scored five runs in the series. Baltimore won the opener 2-1, then lost 3-1 before rallying to win the finale.

"I thought we played a good series but came out on the losing end," Washington's Ian Desmond said. "No one in here is searching for any confidence."

After Wieters gave Baltimore the lead, he sealed the victory in the ninth. With one out, Jim Johnson struck out Danny Espinosa and Wieters threw out Desmond attempting to steal second base.

"Any out you can get, especially the 27th out, is huge," Wieters said.

Orioles manager Buck Showalter considered resting his workhorse catcher, who also played Saturday night, then decided against it.

"I came close to not playing Matt, with an off-day (Monday)," Showalter said.

The Orioles finished 11-7 in interleague play and won five of six series.

Pedro Strop (4-2) got the final out in the eighth for Baltimore and Johnson worked the ninth for his 22nd save.

Making his first start for the Nationals since May 25, Ross Detwiler allowed four hits and walked two in five innings. In his previous start against Baltimore on May 19, the left-hander gave up six runs. But that was at a point in the season when the Orioles scored 32 runs over a six-game span.

Jake Arrieta gave up one run and five hits in six innings, and it still took an unlikely comeback by the Orioles for him to avoid becoming the first 10-game loser in the big leagues this season.

Zimmerman snapped a 5-for-49 slump and gave Washington the lead with a two-out single that scored Jhonatan Solano. Zimmerman, who went 2 for 4, hopes the cortisone shot will help.

"We just decided that would give me a chance to continue to play and not miss any more time," he said. "It took that pain and pressure away from me that has been bothering me for a while. It's a test case."

Detwiler retired his first seven batters and was cruising until the fourth, when Baltimore loaded the bases with two outs. Ronny Paulino hit a harmless fly ball to end the threat.

In the Orioles fifth, two singles and a groundout put runners on second and third with two outs for Jones, who hit a fly ball to deep left.

Bryce Harper led off the Washington sixth by turning a bouncer up the middle into a dash-for-second double, but Arrieta worked out of trouble by getting Desmond to hit a two-out popup.

Baltimore's frustration continued in the seventh, when J.J. Hardy grounded out with runners on second and third and two outs.

NOTES: On Monday night in Colorado, Washington RHP Stephen Strasburg vies to become the first player in Nationals history to win seven consecutive starts. ... The Orioles open a two-game series against the Los Angeles Angels on Tuesday. LHP Dana Eveland likely will begin paternity leave on that day, and it's possible that RHP Matt Lindstrom (finger) will be activated from the disabled list to fill out the Baltimore roster. ... Nationals closer Drew Storen, who had elbow surgery in April, hopes to make his season debut next weekend in Atlanta. ... Held out of the starting lineup in part because of an 0-for-28 slump, Baltimore's Chris Davis flied out as a pinch hitter. ... The Orioles have gone 17 straight games without a stolen base, their longest such streak since a 20-game run in June 1962.