WASHINGTON — So much for the plan to have Manny Acta's patient optimism lead the Washington Nationals out of the doldrums. The abysmal won-loss record became too much to stomach, costing him his job at the All-Star break and adding another layer of instability to the worst team in baseball.

Acta was fired after the team reached the unofficial halfway mark of the season with a 26-61 record, on pace to clear the 100-loss mark for the second consecutive year. Acting general manager Mike Rizzo — himself an interim placeholder — announced Acta's dismissal Monday morning.

"We feel that the team has underachieved," Rizzo said. "We feel we have a better ballclub than we've shown on the field. ... We feel with a different voice and possibly a different feel in the clubhouse that we can have a more successful second half of the season."

Acta was informed Sunday night after the team returned home following a 5-0 loss at Houston, Washington's seventh in 10 games. Bench coach Jim Riggleman, who has a 522-652 record over nine seasons managing the Padres, Cubs and Mariners, was named the interim replacement — which means the Nationals now have both a GM and a manager with a temporary label next to their names.

"I'm very uncomfortable with that," team president Stan Kasten said. "I've strived my whole career valuing stability and consistency, and I want to get to that here. We're not there yet. I think we're working toward that. Sometimes you encounter these unfortunate, unforeseen bumps in the road."

Acta joins Colorado's Clint Hurdle and Arizona's Bob Melvin as major league managers who have been fired this season.

"It was a great learning experience, I have no regrets," Acta said in a statement released by the team. "As I move forward, I wish the Nationals all the best. I was very fortunate to work with and meet a lot of wonderful people while here."

Acta was 158-252 over 2½ seasons in his first managerial job. The team's winning percentage dropped progressively from Year 1 until now, although his record had much to do with the talent — or lack thereof — assembled for him by the front office. The Nationals opened this season without anything close to a reliable bullpen and fielded a lineup with numerous defensive liabilities. For a while, the starting pitching rotation consisted of four rookies and one second-year player.

Not surprisingly, the Nationals' 5.21 ERA is by far the worst in the National League, and their 82 errors are the most in baseball.

"I'm not satisfied with the way we play the game at times," Rizzo said. "We don't execute nearly as often as I expect them too. But the effort as far as the hustle and preparation is there — the consistency of the effort and the hustle needs work. The way we fundamentally play the game needs a lot of work."

Zimmerman, speaking at the All-Star festivities in St. Louis, echoed Rizzo's theme.

"The only problem with our team is that there's not that sense of urgency to win," Zimmerman said. "I think we're better than what we've shown. Maybe this will wake some people up.

"Some people there are so used to losing they don't have that fire to win. I think there needs to be accountability and some responsibility taken. We have the built-in excuse of being young, but we're not that young anymore."

Yet Acta always remained upbeat, preaching patience and emphasizing the importance of keeping an even keel — so much so that some wondered whether he needed to show more fire and perhaps be more critical publicly when his players made mistakes. Rizzo said Acta's style made it more difficult for the team to recover from an 0-7 start.

"The response was from a slow start out of the gates, and then getting into a hole that they felt they couldn't get out of, I think that was a big part of it," Rizzo said. "And sometimes the even-keel-ness plays into that by not being a little more vocal, a little bit more hard-edged."

By contrast, Rizzo also called Riggleman "a tough disciplinarian" who is "going to show the young players that this is a difficult game to play." Rizzo said Riggleman, who will not hold his first news conference until Wednesday, "will be a candidate to be the long-term answer" as manager.

Acta's firing is only the latest example of the constant upheaval surrounding the Nationals since Kasten and local developer Ted Lerner took over the club during the 2006 season — a sale that was supposed to finally bring a semblance of normalcy to the franchise.

When Acta was hired in November 2006, he was 37, and no manager in the majors was younger. In his first season, Washington finished 73-89, fourth in the NL East and better than was expected. Acta even received votes for NL Manager of the Year.

But the team took a step backward in 2008, going 59-102, the worst record in the majors. Every coach except pitching coach Randy St. Claire was fired at the end of the season, and St. Claire was dismissed at the beginning of June. At spring training this season, Acta called the current team the most talented he's had, but the Nationals never came close to approaching .500.

Still, Kasten took a page out of Acta's optimistic book Monday as he spoke about a young talent base, saying he thinks the team is "very close to realizing the fruits of three hard years of effort." The team's ownership group also issued an upbeat statement to fans.

"We know we have a way to go, but the end result will be all the richer for the early days we've spent together at Nationals Park," the statement said. "We are getting better. We want you to be with us as the pieces of the puzzle come together."

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AP Sports Writers Howard Fendrich in Washington and Ronald Blum in St. Louis contributed to this report.