In a press conference on late Monday morning, Rizzo said a change needed to be made because the team underachieved in the first half of the season. The Nationals went into the All-Star break with an MLB-worst 26-61 record.
"This was a decision that we finalized over the weekend with the management team here in Washington," Rizzo said. "We feel that the team has underachieved. We feel that we have a better ballclub than we've shown on the field -- 26-61 is unacceptable to not only the Lerner [ownership] family, but to Stan Kasten and myself and the ballclub.
"We feel that with a different voice and possibly a different feel in the ballclub, we can have a more successful second half of the season. We think we have pieces in place here to have some type of success. We also acknowledge our flaws as a ballclub, and we're working hard before the trade deadline to address the flaws and make prudent baseball deals to address the flaws."
This will be Riggleman's fourth managerial job. He's posted a 622-652 career record in previous stints with the Padres, Cubs and Mariners.
Riggleman's best season as a skipper was in 1998, when he guided the Cubs to the playoffs after Chicago won a Wild Card tiebreaker over the Giants. The team lost to the Braves in the National League Division Series, 3-0.
Riggleman, who was not at the press conference, is scheduled to have a workout at Nationals Park on Wednesday evening.
"Jim Riggleman is a terrific baseball person," Rizzo said. "He's a baseball guy from the old school. He's a guy with nine seasons of experience as a Major League manager, and he's a guy that we -- I -- respect greatly.
"He certainly will be a candidate to be the long-term answer as the manager."
Acta managed the Nationals for two-plus seasons and compiled a 158-252 record. The Nationals currently have the youngest starting rotation in baseball -- all five pitchers are 25 years old or younger -- but it was a struggling bullpen and a porous defense that were the major reasons for the disappointing record.
"It's unfortunate how things turned out," right-hander Jason Bergmann said. "We probably had our best team in the last couple of years. Unfortunately, we had the worst record, too."
Said outfielder Josh Willingham: "It's not Manny's fault. It's kind of the nature of the business. When a team struggles, you can't fire 25 players.
"If you look at the beginning of the season, our offense was on fire, but we couldn't keep teams from scoring. That's how we lost. Then, in the latter part of the first half, the problems were more hitting-related. We had problems with runners in scoring position and our pitching got better. It's a combination of not putting it all together. Good teams play great defense, pitch well and hit in a timely matter with people on base."
With Riggleman as the manager, Pat Corrales will be the bench coach. This will be Corrales' second tenure with the club. The previous two years he had the same role under Manny Acta before being dismissed by former general manager Jim Bowden.
According to one source, the Nationals have contemplated letting Acta go since late May, but decided, first to relieve Randy St. Claire of his duties as pitching coach on June 2. Washington hired Steve McCatty to replace St. Claire.
Acta was not at the news conference, but did release statement the following statement:
"First, I would like to thank God for putting me in this position. I want to thank the Washington Nationals for giving me the opportunity to be a Major League manager. It was a great learning experience, I have no regrets.
"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.
"I'd like to extend a special thank you to the fans for being so patient and supportive over the last two and a half years.
"Last but not least, to the media, thank you for being fair and respectful toward my family and I."
Kasten, Rizzo and Riggleman were expected to meet on Monday afternoon to talk about the second half of the season. Kasten is optimistic that the Nationals will turn things around.
"We're going to start the Riggleman era on Wednesday and will provide him to you all then," Kasten said. "We had a lot of mechanics and things to accomplish since midnight last night when we had our meeting with Manny.
"Every media report I've seen has said, 'Gee, the talent there should produce a better record than 26-61.' I think all of you believe that. I do think it should start producing wins very, very soon, especially now that we're getting pretty consistent starting pitching."