Nigel Pearson's side took advantage of the inactivity of QPR and Burnley to extend their lead at the summit with a seventh successive league win - a run that equals their club record.
Jamie Vardy opened the scoring in the 52nd minute and although David Nugent saw his penalty saved by Shay Given 18 minutes later, Ritchie de Laet doubled Leicester's advantage soon after as the visitors' six-match unbeaten league run came to an end.
Fourth-placed Derby County failed to make significant ground on the top two as they needed a late goal to claim a point from a 1-1 draw at Blackburn Rovers.
Rudy Gestede put the hosts ahead two minutes after the break, but Patrick Bamford earned his side a share of the spoils with an equaliser six minutes from time to make it two goals in two appearances since signing on loan from Chelsea.
Ipswich Town moved up to seventh with a 2-0 home win over Reading, Daryl Murphy and substitute Paul Anderson with the second-half goals as Mick McCarthy's side won for the first time in five matches to move within two points of their opponents in the final play-off berth.
Elsewhere, Billy Sharp marked the start of his second spell back at Doncaster Rovers with an 85th-minute equaliser to earn his side a point in a 1-1 draw at managerless Blackpool.
The hosts, who parted company with Paul Ince earlier in the week, went in front through Andy Halliday's 78th-minute goal, but Sharp hit back seven minutes later as Blackpool's winless league run was extended to 10 matches.
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