(Sports Network) - The bats have been decent and the starters are keeping them in the games, but credit for the Washington Nationals' current winning streak belongs to the bullpen.

Washington has won six of its last seven games, including a season-high four straight, to get to 12-17 on the season. Though still in last place in the National League East heading into play on Friday, the Nationals have yielded three or less runs in each of their last five victories.

Over those last five wins, Washington's bullpen has allowed just three runs over 14 innings of work, which is good for a 1.93 earned run average. Jon Rauch has been the best of the bunch, posting a win, three saves and just one hit allowed in 2 2/3 innings. Saul Rivera has picked up a pair of wins as well.

Washington's starters have been doing their part, they just don't have the wins to show for it. None of the hurlers have allowed more than two runs in each of the last five victories, but only John Lannan walked away with a win, defeating the Cubs on April 27. Washington's starters have a 1.85 ERA over the last five wins.

Odalis Perez has posted back-to-back two-run starts, but didn't factor into the club's triumph over the Cubs on April 25 or versus the Pirates on Thursday. Perez has a solid 3.18 ERA on the season despite being 0-3.

"What he has done for us has not gone unnoticed, despite the fact that he doesn't have a win, we are very satisfied with what he has given us so far," said Washington manager Manny Acta after the team's victory over Pittsburgh.

The Nats' team ERA (4.27) is now ranked 10th in the NL, while the bullpen's 4.16 ERA is 11th in the Senior Circuit. The pitching staff's recent run of success is helping compensate for Washington's .229 team batting average that is second worst in all of baseball.

CORDERO BACK ON DL

Chad Cordero was placed on the disabled list for a second time this season on Friday. After spending the first three weeks of the year on the DL due to right shoulder tendinitis, the Washington closer is now expected to miss 4- to-6 weeks because of a tear in his right shoulder muscle.

Cordero had an MRI on Wednesday that revealed the tear, just one day after getting charged with a run and two hits in just a third of an inning versus the Braves. Rauch came on and allowed an inherited runner to score, but got the final two outs to record the save.

Cordero has worked in six games this season, recording a 2.08 ERA in just 4 1/3 innings.

Rauch is more than capable in taking over the closer role, as the 6-foot-11 right-hander is 2-0 with a 3.77 ERA and six saves on the season in 15 appearances.

With an open roster spot, the Nationals activated catcher Paul Lo Duca from the 15-day DL. Lo Duca hasn't played since April 13 due to a bruised right hand. He was hitting just .200 (7-for-35) with four runs batted in and four runs scored on the season before the injury.

WHO'S HOT

In addition to the entire Washington bullpen, Ryan Zimmerman deserves a mention after hitting the 47th homer of his career on Tuesday against Atlanta. That allowed him to pass Alfonso Soriano (46 homers) for most on the club since it moved from Montreal to Washington DC.

WHO'S NOT

Austin Kearns is batting just .158 (3-for-19) over his last five games, dropping his season average to .194 to go along with two homers and 11 RBI. The right-handed hitter did go 2-for-4 on Thursday versus Pittsburgh, driving in the winning run in the eighth inning.

ON DECK

Washington continues its four-game set with Pittsburgh on Friday, as Matt Chico (0-5, 6.68 ERA) goes against Phil Dumatrait (0-1, 3.92). Saturday will pit John Lannan (2-2, 2.64) against Paul Maholm (2-2, 3.26), while Tim Redding (3-2, 3.55) pitches Sunday's finale versus Ian Snell (2-1, 4.93).

Washington wraps an 11-game homestand with this series against the Pirates. After an off day on Monday, the Nats play three straight in Houston.