LOS ANGELES -- The Nationals called up first baseman/outfielder Tyler Moore from Triple-A Syracuse and placed infielder/outfielder Mark DeRosa on the 15-day disabled list on Sunday.

Moore started in left field after Jayson Werth was a late scratch from the lineup because of a migraine headache, with Bryce Harper sliding over to center for the series finale. Moore was 1-for-3 in a 2-0 loss to the Dodgers.

"I was trying to get a win today. It didn't happen," Moore said. "It was a great day [to be in the big leagues], it was fun. It was everything I hoped it was going to be."

The move to promote Moore comes a day after the team's No. 1 prospect, Harper, was called up to the big leagues.

Moore, who is ranked No. 14 on MLB.com's list of Top 20 Nationals prospects, was having a better season at Syracuse than Harper. Moore was hitting .286 with seven home runs and 20 RBIs before getting recalled.

In the last two years, Moore has hit a combined 60 home runs with 201 RBIs for Class A Potomac and Double-A Harrisburg.

The move to call up Moore comes two days after general manager Mike Rizzo said Moore was not ready to play left field in the big leagues.

"The decision is a team decision," Rizzo said Friday of why the club promoted Harper over Moore. "It supports the Major League club. We need an offensive player that can play the corner outfield. It was a choice between a couple of players on the farm. Tyler Moore just didn't have the experience to play left field at the Major League level yet. He just started to play there several weeks ago."

The Nationals changed their minds Saturday. Moore, 25, most likely will come off the bench and spell Harper in left and Adam LaRoche at first base, but manager Davey Johnson declined to say what his plans were for Moore. Johnson will likely make an announcement on Tuesday before the Nationals play the Diamondbacks.

"I'm real excited for him," said infielder Steve Lombardozzi, who played with Moore throughout their Minor League careers. "Physically and mentally, he is impressive -- his mindset, his approach, and just what he can do on the field. He is an athlete. He is a strong, strong guy. He is fun to play with."

As for DeRosa, he was placed on the DL because of a left oblique strain. He started feeling the pain Saturday while he was doing his outfield drills. DeRosa, 37, didn't think anything of it, but the injury became worse after he took batting practice.

"That's when I felt it pretty good," DeRosa said. "Great start to the year for the Nationals, but a horrible start to the year for me."

DeRosa, who will get an MRI on Monday in Washington, said he has never had an oblique injury in his career. Before signing with the Nationals, DeRosa had serious left wrist problems that made him miss most of the last two years with the Giants.

"The last 2 1/2 years have been frustrating," he said. "I'll deal with it and get back. We're in first place and we are playing well. It's frustrating because you work so hard. As they say, the older you get, the harder you have to work. I came back from a major injury. The body won't give me a break, for whatever reason."

The veteran was off to a slow start, going 3-for-37 (.081) with two RBIs. He said the oblique injury had nothing to do with his slow start.