WASHINGTON -- After allowing five runs in only one inning the past two games, Brad Lidge is no longer a member of the Nationals' bullpen.

Washington designated the right-hander for assignment before Sunday's series finale against the Yankees and activated 28-year-old Ryan Mattheus from the 15-day disabled list. Mattheus returned to the Nationals' clubhouse from his rehab assignment before Saturday's game, in which Lidge took the loss in the 14th inning.

"After his performance yesterday, [Lidge] told me that he kind of knew there would be some kind of move with the bullpen," said general manager Mike Rizzo. "He said he was disappointed with the way he pitched and he was sorry it didn't turn out better."

The Nationals signed the two-time All-Star closer in January, but he posted a 9.64 ERA in 11 appearances with Washington. He spent time on the disabled list with a sports hernia, but Rizzo said both he and Lidge believe the 35-year-old is healthy. Since going a perfect 48-for-48 in save chances during the Phillies' 2008 World Series championship season, Lidge is 1-12 with a 5.08 ERA.

Lidge said he felt like he made good pitches against the Yankees -- who tagged him for three runs in one-third of an inning Friday and two runs in two-thirds of an inning Saturday -- but they just hit the ball where the defense wasn't. Only Mark Teixeira made solid contact against Lidge, but his double into the right-field corner Saturday scored the winning runs.

Entering Saturday, Mattheus had a 2.60 ERA in 54 games since making his Major League debut last season. He allowed five runs in 20 innings this season before landing on the disabled list with plantar fasciitis in his left foot.

"The 14-inning game last night forced us to make a bullpen roster move," Rizzo said. "Brad wasn't performing well. He was very disappointed. Mattheus was ready to come off his rehab assignment, and we felt like this was the right time to make the move."

Storen building arm strength during rehab

WASHINGTON -- Drew Storen threw 30 pitches off a mound three times last week, and he expects to do the same this week while increasing his pitch count. He is throwing only at a 75-percent effort level as he attempts to build arm strength after April surgery to remove bone chips from his right elbow.

The 24-year-old closer remains on pace for a return around the All-Star break.

"I haven't had any pain and it feels like it's getting stronger every day, so there's legitimate improvement," Storen said. "The last bullpen I threw [Friday] was probably the best I felt. I'm feeling really good, my command is good and my mechanics are still there. I'm very happy with where I'm at."

Doctors targeted an All-Star break return for Storen as soon as he had surgery, but Storen said he is actually progressing ahead of schedule.

He expects to work his pitch count up to 50-60 pitches at a lower effort level, even though he never threw more than 35 pitches in a game in two years in Washington. He plays catch or long tosses every day between bullpen sessions.

"It's kind of one those things where you have to be able to jog before you sprint," Storen said. "I have to be able to get that arm strength up, and that's what you do with 50-percent bullpens for 50 pitches ... before you start giving max effort."