NEW YORK -- The Nationals selected the contract of right-hander Livan Hernandez and optioned right-hander Garrett Mock to Triple-A Syracuse on Sunday.

Hernandez started against the Mets that same day and is expected to be the fourth starter in the rotation. Because Hernandez had a Minor League contract, the team decided to start the season with eight relievers and wait to activate Hernandez until his first start.

As for Mock, he was put on the 25-man roster even though he did not pitch well in his final three Spring Training starts, including a Minor League game against the Astros. The organization told Mock nine days ago that he would be on a short leach, and the team was not afraid to call up another pitcher if he didn't perform.

Mock didn't perform well Friday against the Mets, allowing two runs in 3 1/3 innings and walking five batters. Mock claimed he had problems throwing the ball in the windy conditions at Citi Field. It was obvious, however, that his reasoning didn't go over well with the club.

Simply, the Nationals wanted Mock to get his sinker down and throw more strikes.

"This is a performance league. We need guys to perform," general manager Mike Rizzo said. "We are here to win games. Garrett has to iron out some mechanical things to allow him to throw more strikes. The bottom line is, he'll have to perform. He has to go more than 3 1/3 innings and you have to give your ballclub a chance to win. He didn't do that through the tail end of Spring Training and in his first start. We have guys who have pitched well at the end of Spring Training and pitched well to start the season."

Mock was stoic when he talked to the media about his demotion, but he sounded like a man who understood why he is being placed on the Syracuse roster.

"It's encouraging the way the team is going," Mock said. "They are not going to put up with what I did in my first game. They are going to get somebody else in here to do [the job]."

With Mock gone, the Nationals will promote left-hander Scott Olsen in time for Thursday's game against the Phillies.

Olsen didn't make the 25-man roster because the team wanted him to build arm strength after having shoulder surgery last summer. In his first start for Syracuse, Olsen pitched 6 1/3 innings and gave up four runs on eight hits. He didn't figure in the decision. While the numbers didn't look great, it appears that Olsen's fastball is back where it should be.

"[Assistant general manager] Bob Boone was there, and he said he looked really good," Rizzo said. "His stuff looked much better than his numbers. It looks like he is getting back -- healthy wise and stuff wise. That's what we were looking for."

Morse goes on DL; Bernadina back in the bigs

NEW YORK -- The Nationals placed outfielder Mike Morse on the 15-day disabled list because of left calf strain and recalled outfielder Roger Bernadina from Triple-A Syracuse.

Morse hurt the calf while making a catch Wednesday against the Phillies. He was available for pinch-hitting duties after that game, but couldn't do much else. Morse insisted that the injury is getting better and should be 100 percent once it's time to be activated from the DL.

With Morse out, the Willie Harris/Willy Taveras platoon in right field is back in full swing. Taveras helped himself by driving in four runs against the Mets on Saturday, while Harris continues to make great defensive plays.

Bernadina will get occasional starts against right-handed pitching. Bernadina joins the Nationals after going 6-for-15 (.400) with a homer and two stolen bases in three games with Syracuse.

Zimmerman likely out until Wednesday

WASHINGTON -- Third baseman Ryan Zimmerman is not expected to play on Sunday or Monday because of a tight left hamstring. With Tuesday being an off-day, the Nationals hope that Zimmerman is back in action Wednesday.

"We are trying to get it better than trying to play through it," Zimmerman said. "I think it's smart to do what we did. We'll get it better and be ready for the full season.

English remains in the big leagues

WASHINGTON -- With the Nationals having eight relievers, it was assumed that that left-hander Jesse English would be sent down once right-hander Livan Hernandez was called up to the big leagues. Besides having options, English has the least experience among the relievers on the 25-man roster.

But after a disheartening lost to the Mets on Friday, members of the Nationals' front office were in meetings and decided that day that English would not be optioned to the Minor Leagues. The team still wants two lefties out of the bullpen.

Entering Sunday's action, English had given up two runs in 1 2/3 innings. English said he has to stop pitching behind in the count.