Coventry City are three points off the relegation zone after the defeat at Gillingham.
City's 3-1 loss leaves them three points ahead of Crewe who lost 2-1 at Notts County, five points ahead of Colchester who lost 2-0 at home to Walsall, five points ahead of Crawley who lost 4-1 at fifth placed Rochdale and six points clear of bottom side Yeovil Town who beat sixth placed Bradford City 1-0.
The Sky Blues are seven points off the play-offs but will need to improve their goal difference of minus ten if they are to take over Bradford City.
Swindon stay top on goal difference after a 3-1 win over Chesterfield. Bristol City, who won 2-0 at Scunthorpe are second with MK Dons who beat Sheffield United 1-0 in third.
Elsewhere, Doncaster beat Barnsley 1-0, Oldham won 2-0 at Fleetwood and Port Vale beat Peterborough 2-1.