There’s little doubt that the milers throughout the state will have to keep a watchful eye on Mancheser/Essex’s Olivia Lantz this winter. Just being aware, though, of the talented sophomore won’t necessarily mean she’ll be any easier to defeat. Lantz looked to be in mid-season form as she switched gears at 800 meters and ran the second half of the mile in 2:31 for a sterling 5:11.72 in yesterday’s MSTCA Winter Festival Small Schools Invitational at the Reggie Lewis Center. Lantz dueled with Jane Clark of Notre Dame of Worcester over the final 600 meters before pulling just ahead on the back straightaway. Clark ran a superb 5:12.31 for second while Taylor Worthy of Medfield was also under the 5:20 mark in 5:18.52.