JUPITER, Fla. -- The Nationals have decided not to terminate the contract of left-hander Scott Olsen, according to a baseball source.

The club did not confirm that Olsen will stay with the Major League team. It had until Wednesday to let him go or pay him a full base salary, which is $1 million.

The Nationals could have saved $750,000 had they let Olsen go, but they feel he has a lot to offer to the organization. Olsen will either start the season as the fifth starter in the rotation or with Triple-A Syracuse.

Olsen helped himself Sunday by having a quality start against the Braves. Olsen pitched 5 1/3 innings and gave up one earned run on seven hits. He struck out four and walked none. It was clearly Olsen's best outing of the spring.

Olsen's numbers don't tell the whole story. The Nationals noticed that Olsen threw harder Sunday than he did this entire spring. Olsen has been building up arm strength since having shoulder surgery last July. Washington did not keep velocity readings on Olsen on Sunday.

Now, Olsen finds himself competing against right-hander Garrett Mock for the final spot in the rotation. Olsen will pitch against the Red Sox on Friday, while Mock doesn't have any more starts left. In his last outing, Mock was hit hard, allowing four earned runs to the Marlins in 4 2/3 innings on Tuesday.

After Olsen's appearance against Boston, the Nationals decide whether Olsen or Mock is going north with them.

"Our fifth starter is down to those two guys," manager Jim Riggleman said. "Basically when Olsen pitches, it will help us determine whether Olsen is the fifth starter or Mock is the fifth starter. Somebody is going to get the job, but nobody has won it."

The Nationals have already determined the rest of their rotation. John Lannan will be the Opening Day starter against the Phillies on Monday. Jason Marquis, Craig Stammen and Livan Hernandez will follow.