This was a few months ago, during a break in the two-day general managers meetings in Indian Wells, Calif. Ben Cherington had not yet made a single change to the Red Sox roster, but as he stood outside the doors of a hotel ballroom, he already realized the stark reality of the cleanup from last season’s 93-loss train wreck. “The best way to get better,” Cherington said, “is to see improvement from the guys we have.” That’s especially true for the pitching staff. The Starters Last season, Red Sox pitchers combined for the American League’s third-worst ERA (4.70) and fifth-worst WHIP (1.37). None of the starters ranked above the league average in either category. Yet in replacing more than one-third of the roster this offseason, Cherington added only three pitchers, including just one starter. And although hopes are high for right-hander Ryan Dempster, the Sox know the 35-year-old isn’t such a big difference-maker that he single-handedly will improve a rotation that compiled a 5.19 ERA. Jon Lester, on the other hand, could have that effect. It isn’t an overstatement that the Red Sox’ revival is tethered to Lester’s left arm. The two-time All-Star has slipped over the past two seasons, bottoming out last year with 14 losses and a career-worst 4.82 ERA. Since 2010, his hits-per-nine innings stat has risen from 7.2 to 7.8 to 9.5, while his strikeouts-per-nine innings number has dipped from 9.7 to 8.5 to 7.3. So, all eyes will be on Lester and, to a slightly lesser degree, Clay Buchholz. If their struggles last season were merely aberrational, the Sox will be well-positioned for a turnaround. But if 2012 is their new normal, well, cover your eyes. “If they pitch to their capabilities, they have the ability to lead any staff,” said new manager John Farrell, the pitching coach with whom Lester and Buchholz had their best years. “There’s unified confidence that both of those guys, because they are healthy and they are talented, the ingredients are there to be successful pitchers.”