ATLANTA -- The Nationals overhauled their bullpen during the offseason with the hope of eradicating the problems that plagued them throughout all of last season. The only member of this year's Opening Day bullpen remaining from the Opening Day bullpen in 2015 is right-hander Blake Treinen.
It was only the first game of the 2016 season, but Monday's 4-3 victory against the Braves in 10 innings offered glimpses of the roles manager Dusty Baker envisions for the Nats' new-look bullpen this season. Most of the unit's roles remain unclear, with the exception of Jonathan Papelbon, who will be the closer. Baker said during the spring that he would not be able to settle on bullpen roles until he had a chance to see how players responded when put in those situations.
The Nationals struggled finding a reliable setup man late last season, and the team has high hopes that left-hander Felipe Rivero -- 24 years old and armed with an average fastball velocity of 95.5 mph -- can build off an impressive rookie season and fill a late-inning role this year despite his lack of experience in that capacity. Baker has been impressed with him since the start of Spring Training, and the manager turned to Rivero in a tie game in the eighth inning. Rivero struggled on Monday, however, allowing a walk and a single and hitting Freddie Freeman with a pitch, and he exited the game with two outs and the bases loaded.
"He just wasn't that sharp," Baker said.
In high-leverage situations with runners on base, Baker figures to turn to Shawn Kelley, the veteran right-hander who signed a three-year deal in the offseason. Entering Monday's game, Kelley had allowed only 20 percent of inherited runners to score over the past three seasons.
"That's the lowest on our team," Baker said. "And that's why we brought him in there, for that situation. But sometimes, as you see, the stats don't follow suit."
Kelley replaced Rivero, and his first four pitches to Adonis Garcia missed the strike zone by a wide margin for a bases-loaded walk that forced in the go-ahead run.
Baker called upon left-hander Oliver Perez to face the next batter, lefty Nick Markakis. Perez held lefties to a .517 OPS last season and figures to slot into the lefty specialist role for Baker. Perez did that job well Monday, striking out Markakis to prevent further damage. Down a run, Washington rallied in the top of the ninth to tie the game off Atlanta right-hander Jason Grilli.
Baker likes Treinen's ability to get out of jams with his sinker, as Treinen did when he entered the game in the bottom of the ninth. He walked the leadoff batter and then promptly erased the baserunner by inducing a double-play grounder. Treinen also has the ability to pitch at least two innings in relief, which could have been the plan had Monday's game continued.
But the Nationals scored in the 10th and turned the game over to Papelbon, who tossed a scoreless inning to seal the victory. The outing underscored the fact that Papelbon -- for all the ire he has drawn from Nats fans for replacing fan favorite Drew Storen, as well as for grabbing Bryce Harper by the throat last September -- will be a valuable member of the team's bullpen this year. Washington is counting on Papelbon to pitch to the form that made him an All-Star last season, and the club can ill afford more uncertainty in the bullpen.
Jamal Collier is a reporter for MLB.com. Follow him on Twitter at @jamalcollier. This story was not subject to the approval of Major League Baseball or its clubs.