Chesterfield moved into the League One play-off positions with a 1-0 win over rivals Bradford in a scrappy game at Valley Parade.The Spireites,who began the match level on 54 points with 10th placed Bradford but a position higher because of more goals scored, won the match with a goal in first half stoppage time by Byron Harrison following a mistake by home defender Gary MacKenzie.Harrison intercepted MacKenzie's weak headed back pass to keeper Ben Williams and slotted the ball home from close range.Sam Hird also had the ball in the net for the visitors in the 50th minute but was ruled offsideBradford, who used all three substitutes, could make little impression on Chesterfield defence as they battled for a second half equaliser although they came close in the 89th minute when goalkeeper Tommy Lee blocked substitute Tony McMahon's effort with his legs.