PORT ST. LUCIE, Fla. -- With Johan Santana almost certain to begin the season on the disabled list, the Mets officially named lefthander Jon Niese their starter for Opening Day on April 1 against the Padres.

"I put a lot of hard work into becoming a starting pitcher, and to become the Opening Day starter, it means a lot,'' Niese said Thursday. "By no means do I want to say that I'm the leader of the staff. Obviously, Johan and [Shaun] Marcum do a very good job of that. But obviously, now that I'm in this role, I'm just going to do the best I can to compete.''

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Niese, 26, went 13-9 with a 3.40 ERA last season and has pitched well in spring training.

Said general manager Sandy Alderson, "He's matured tremendously over the last couple of years and I think he very definitely deserves the opportunity to start on Opening Day.''

Meanwhile, the Mets have all but officially put Santana on the DL to begin the season. He is long-tossing to build strength in his surgically repaired left shoulder, though he's several steps from appearing in an exhibition game.

When asked if Santana is bound for the disabled list, Alderson said, "I'm not prepared to say that today, although I think that's extremely likely.''

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Notes & quotes: Marcum (right shoulder impingement) called the cortisone shot he received a "precautionary measure.'' He expects to pitch again in camp . . . In his first game back, infielder Justin Turner (ankle sprain) had a pinch-hit single in a 3-2 loss to the Cardinals.