In addition, the Nationals dealt first baseman Nick Johnson and $1.5 million to the Marlins for pitcher Aaron Thompson. This particular deal was made 17 minutes before the non-waiver Trade Deadline.
"We added starting pitching and a late-inning reliever," interim general manager Mike Rizzo said. "We are not rebuilding. We are building. We are not far from being a good team."
Beimel, who had a 3.40 ERA in 45 games, will be a free agent after the season and the Nationals were not going to offer him arbitration.
"I'm excited. It's a chance to go pitch for a team that is competing," Beimel said. "They are a game back in the Wild Card. Hopefully, I could go there and get to the playoffs with them.
"I kind of expected this trade to happen, but I kind of didn't. I didn't know what to think. As the hours kind of ticked away, I pretty much figured if things were not going to happen I would just stay here. Within 10 minutes of me thinking that, I get a call and I find out that I've been traded. "
The Nationals continue to add pitching to their Minor League system. They added Mattheus even though he is recovering from reconstructive surgery on his elbow. He was 1-3 with a 3.81 ERA in 19 appearances for Colorado's top three affiliates this season before having surgery performed in early July.
In 26 innings prior to the surgery, Mattheus averaged 9.3 strikeouts per nine innings pitched en route to recording a .250 (24-for-96) batting average against.
"He is worth the risk," Rizzo said.
Fabian, who is going to Class A Hagerstown, was 3-6 with a 6.24 ERA in 24 games with Class A Asheville. In 83 2/3 innings, Fabian logged 54 strikeouts and walked just 21, good for a 2.6/1 strikeout-to-walk ratio.
As for Johnson, he didn't think he was going to be traded. When the clock struck 4 p.m. ET -- the Deadline -- he was taking batting practice in the batting cage. About 15 minutes later, interim manager Jim Riggleman called him into his office to inform him that he was traded to the Marlins.
Johnson, who was the last remaining member of the Expos still on the 25-man roster, played in 98 games for Washington and hit .295 with six home runs, 44 RBIs and a .408 on-base percentage.
"It's part of the game," Johnson said about being traded. "You hear certain things. At At 4 o'clock, I went into the cage, and I didn't think it would happen until I got a tap on my shoulder."
Before the trade, the Nationals were trying to sign Johnson to an extension, but the two parties realized that they couldn't come up with a deal before the Deadline. Though the Deadline has passed, they can still make trades, but players involved must pass through waivers.
According to baseball sources, Johnson wants a two-year deal and to make more money than the three-year, $16.5 million extension he signed during the spring of 2006. MLB.com approached Johnson twice about his contract status earlier on the week, but he declined to comment.
"He was a free agent after the season," Rizzo said. "After a few attempts to extend his contract, we thought it would be better for the organization to trade him and get the prospect that we want. Then, [the Nationals will] decide over the winter if we wanted to go after him free agent-wise, or not."
Johnson has had an injury-plagued career during his time with the Nationals/Expos. He has played only two full seasons -- 2005 and '06 -- during his time with the team.
Asked what he would remember about his time with the Nationals, Johnson said: "There are a great bunch of guys, great fans, and I went at it hard every day. I know we didn't win a lot of games, but we pushed forward and competed. I had a good time."
With Johnson gone, Adam Dunn will be the everyday first baseman. Riggleman wasn't sure who would be the backup. He didn't rule out Josh Willingham or Ronnie Belliard playing the position.
Who will replace Dunn in the outfield will not be known until after Friday's game. The Nationals are expected to make two callups, and outfielder Elijah Dukes could be one of the players who receives a promotion. Entering Friday's action, Dukes is hitting .288 with three home runs and 10 RBIs for Triple-A Syracuse.
As for Thompson, he will go to Double-A Harrisburg. A former first-round pick in the 2005 First-Year Player Draft, Thompson went 5-9 with a 4.11 ERA in 20 starts this season for Double-A Jacksonville. Entering this season, he was recognized by Baseball America as having the "best changeup" in the Marlins' system.
In 95 career games, Thompson has posted a 22-34 mark with a 4.00 ERA and 2.26/1 strikeout-to-walk ratio in 506 innings.
"The Nick Johnson trade was made because we got the prospect that we wanted in return," Rizzo said. "There was a reason it went until a few minutes before the Trade Deadline. We knew the player we identified as the guy we wanted. We waited for him. The Marlins came back to us at 17 minutes before the Deadline and gave us the player we wanted."
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.