In the 2010/11 season Lester scored 17 goals in 43 games (all in home games) as Chesterfield won Football League Two. Later going on to sign a new 2-year contract, keeping him at the club until June 2013. Lester suffered a broken arm against Leyton Orient in September 2011 which kept him out of the side for three months. Lacking both Jack and injured goalkeeper Tommy Lee, Chesterfield's results suffered and the team slumped to the foot of the division. Lester returned to the team in late December but was suspended and missed three further matches after the referee in the home game against Walsall watched recorded footage from the game and saw him strike an opponent. On 30 January 2012 Jack scored the late winning goal at Boundary Park against Oldham Athletic which ensured that Chesterfield reached the final of the Football League Trophy at Wembley, on a 3–1 aggregate score.