PORT ST. LUCIE, Fla. — With Johan Santana sidelined, Jonathon Niese is looking more and more like the New York Mets' opening day starter. Niese gave up one run and two hits in five innings Sunday in the Mets' 2-1 loss to the Atlanta Braves.With Santana still building up arm strength — he hasn't pitched in a single spring training game — Niese appears to be the likely replacement for the April 1 opener against San Diego. "I'm not convinced, but there's certainly a strong possibility that's going to happen," Mets manager Terry Collins said.