An own goal from Craig Morgan gave the Foxes the lead, with Matty Fryatt, Andy King and Steve Howard also getting on the scoresheet.
The pressure on Gary McAlister increased as Leeds United fell to their fifth successive defeat - losing 3-1 at second-placed MK Dons.
Sean O'Hanlon and Aaron Wilbraham converted corners in the first half for the Dons, and although Robert Snodgrass reduced the deficit after the break Wilbraham headed in the third.
Millwall slipped off the pace after being held by rock-bottom Crewe Alexandra in a 0-0 bore-draw at home. The Lions remain third.
Away-day specialists Leyton Orient stretched their unbeaten run to seven league and cup games on the road with a battling draw at Oldham Athletic.
Jason Demetriou forced in the equaliser to make amends for a penalty miss just a few second earlier. Another penalty, from Andy Liddell, had seen Oldham take the lead.
A brilliant hat-trick from on-loan striker Craig Davies fired Stockport County into the play-off places with a 3-1 win over Bristol Rovers at Edgley Park.
Lee Clark's first game in charge of Huddersfield Town brought a home win, with Nathan Clarke and Gary Roberts scoring in a 2-0 success over Hereford United.
Tranmere Rovers bounced back from their midweek Johnstone's Pain Trophy exit at the hands of Scunthorpe to secure a 1-0 home win over Brighton & Hove Albion.
Antony Kay was credited with the winner, which came in second-half stoppage time, with a close-range effort after Chris Shuker saw a shot blocked after an Ian Moore shot rebounded off a post.
Yeovil Town boosted their hopes of avoiding relegation with a 3-2 win at Swindon Town.
Craig Alcock and Lee Peltier scored for the Glovers, whose winner came via an own goal from Jerel Ifil.
A second-half goal from Jason Crowe maintained Northampton Town's impressive form as they beat Carlisle United 1-0 at Sixfields.
Cheltenham Town and Walsall played out a goalless draw at Whaddon Road.