Leicester sank closer to an immediate return to the Championship after West Ham pulled clear of the bottom three with a convincing 2-0 win on Thursday.
Tomas Soucek and a Jannik Vestergaard own goal did for the Foxes before half-time as the Hammers climbed to 15th and 16 points clear of the relegation zone.
Since Leicester won the reverse fixture in Ruud van Nistelrooy's first game in charge in early December, the Dutchman has overseen 11 defeats and one draw in 13 Premier League games.
"The goals we concede are easy goals. It's a reflection of how we played in the first half," said Van Nistelrooy.
"We were way too passive. We are in a situation where we are not winning games and we are in a situation where we are in the bottom three. The pressure is on. We cannot wait and sit back."
West Ham were buoyant after their shock 1-0 victory at Arsenal on Saturday.
Graham Potter's men were well worthy of another three points and could have ran out much more comfortable winners.
"It was a professional performance. Not fantastic, but we are delighted with two wins, two clean sheets and six points," said Potter.
Soucek had the simple task to tap into an empty net after Leicester goalkeeper Mads Hermansen saved Mohammed Kudus' effort from close range on 21 minutes.
Jarrod Bowen then took advantage of slack Leicester defending from a corner just before half-time and his shot deflected off the unfortunate Vestergaard beyond Hermansen.
Evan Ferguson wasted the chance to score his first West Ham goal when his shot was blocked by Wout Faes after the break.
But the home side had already done enough to earn back-to-back Premier League wins for the first time since March last year.
Defeat leaves Leicester still five points adrift of safety in 19th and showing no signs of being able to stop a slide back into the second tier.
kca/jc
