WASHINGTON -- Nationals left-hander Ross Detwiler made his first Major League start on Monday night but didn't figure in the decision, as the Nationals lost to the Pirates, 12-7, at Nationals Park.

Detwiler, Washington's first-round pick in the 2007 First-Year Player Draft, lasted five innings and gave up three runs -- two earned -- on four hits. The key stat to manager Manny Acta was that Detwiler didn't walk a batter.

Prior to Monday, the last time Acta saw Detwiler was early in the exhibition season, and the latter was struggling on the mound. He gave up five runs and walked seven batters in 5 1/3 innings.

"He did a tremendous job for us," Acta said. "No walks, which is exactly what we wanted him to do. It was the only thing we were concerned with. We wanted him to pound the strike zone and he did that."

Monday's game is considered a spot start for Detwiler. He is scheduled to go to Triple-A Syracuse as early as Tuesday to get more seasoning, but the team has not ruled out Detwiler getting another big league start on Saturday against the Orioles. If Detwiler goes to Syracuse, look for right-hander Craig Stammen to make the start against Baltimore.

"We were going to give him around 10 starts in Double-A and move him to Triple-A," acting general manager Mike Rizzo said about Detwiler. "This is a spot start. He is still in a developmental stage of his career. He really has pretty good stuff and we don't want to rush him. But we certainly don't want to retard his progress either by holding him back.

"I told him to go out there, have fun, enjoy it, concentrate and let his stuff take over. We'll see where it takes us after this."

The Nationals didn't play good defense behind Detwiler, making three errors early in the game, but it was the third error that ended up hurting the young left-hander.

With one out in the third inning, it looked like Detwiler had Freddy Sanchez picked off, but first baseman Nick Johnson dropped the ball and Sanchez was able to advance to second.

After Nate McLouth was hit by a pitch, Craig Monroe took a low and outside pitch and drove it over the center-field fence for a three-run homer.

"I didn't think it was out at first, but the ball kept traveling," Detwiler said. "Before you knew it, we were down, 3-0."

But Washington answered back with five runs off right-hander Ross Ohlendorf. Josh Bard put Washington on the board with an RBI double. Three batters later, Johnson hit a three-run homer to give the Nationals a 4-3 lead. Ryan Zimmerman followed with a home run.

Detwiler was in line to be the winning pitcher, but the bullpen's struggles continued. This time it was Garrett Mock and Jesus Colome who couldn't get the job done in the sixth inning.

Mock started the inning off by walking Andy LaRoche and hitting Robinzon Diaz with a pitch. Acta and pitching coach Randy St. Claire were visibly upset.

"You are upset because there is no defense for walking guys," Acta said. "There is no defense for hitting guys. It's one thing getting hits, but we wanted him to throw the ball over plate and give the defense a chance. It's just a trend. They just come in don't throw the ball over the plate. Those pitches were supposed to be away."

Two batters later, Mock gave up a two-run double to Jack Wilson to tie the score at 5.

"Just look at the line score. That's what happens when you get behind guys and walk guys," Mock said.

Delwyn Young, Brandon Moss and McLouth had RBI hits against Colome in the inning. In the last two innings of the game, the Pirates would score four more runs against Nationals relievers.

"It was just sad to see how thing are going with our bullpen," Acta said. "I've been in the game a while, I've just never seen anything like it before. We are going to have to change the mind-set over there. I don't think Mike [Rizzo] or myself want to lose."

How does one change the mind-set of the relievers? Acta believes making more roster moves will solve the team's problems. But the Nationals have done it already. They started the season with a young bullpen; by mid-April, Washington went with a veteran staff.

"Change it up, because it's not working," Acta said.