Wednesday, looking to bounce back after the 2-1 midweek defeat at Watford, were in trouble on seven minutes after conceding a corner on the right.
Midfielder Alan Sheehan pumped the corner over to the far post and centre-back Gareth McAuley rose unchallenged to head in from close range.
Sunderland's on-loan midfielder Graham Kavanagh had a stinging shot blocked and, as the ball rebounded to Deon Burton, the Wednesday striker pulled his low shot wide of the target from 14 yards.
The Hillsborough side blundered again from a set piece in the 14th minute as Leicester added a second - this time at the near post.
Keeper Lee Grant came out to clear another Sheehan corner but punched the ball against striker Akpo Sodje and was helpless as it spun over the line.
Iain Hume tried his luck with a spectacular overhead kick and Sheehan miscued 10 yards out before Wednesday's misery continued as centre-back Michael Johnson limped off.
Veteran defender Lee Bullen almost pulled one back minutes before the interval when his fierce strike from just inside the area took a deflection and the spun inches over the top.
Burton went close with a 20-yard strike and Marcus Tudgay drilled the ball over the top from long range as Wednesday looked for a goal to get them back into the game.
Francis Jeffers was thrown on in place of Burton and Burton O'Brien came on to replace the ineffective Sodje with Tudgay pushed up front as Owls boss Brian Laws juggled his side in an effort to find a way round Leicester's five-man defence.
The breakthrough almost came in the 75th minute when Jeffers slipped the ball inside to O'Brien, whose right foot strike was palmed away by Marton Fulop.