Chesterfield moved closer to promotion when second-half goals from Jack Lester and Deane Smalley settled a scrappy game against Port Vale.
Lester headed his 15th goal of the season just after the interval and Smalley sealed victory with a neatly taken goal in the 71st minute.
Vale weathered an early storm from the runaway League Two leaders in which Craig Davies volleyed against a post to frustrate the home side in a first half littered with misplaced passes.
Marc Richards headed over from close range but Vale created few other chances in a game where Lester's class near goal again proved decisive.
The veteran striker pounced in the 48th minute to put away a cross from Dean Morgan at the back post that Vale failed to deal with.
Vale scrapped hard but any hopes they had of getting back in the game vanished when Drew Talbot played Smalley in and the winger sidestepped Stuart Tomlinson to slide in his 11th of the campaign.