Leicester made it four wins from four under Craig Shakespeare and picked up their first away victory of the season with a 3-2 success at West Ham.
Riyad Mahrez, Robert Huth and Jamie Vardy -- three of the main protagonists of last season's title triumph -- stunned the Hammers with first-half goals.
The Foxes showed no signs of a European hangover following their epic win over Sevilla, and although they may have a quarterfinal meeting with Atletico Madrid on their minds Shakespeare knows they still need to get their domestic affairs in order.
Fortunately they faced a West Ham side playing as though they just want their first season at their new stadium to end as quickly as possible.
Manuel Lanzini briefly halved the deficit with a free kick but they were booed off at half-time, and although Andre Ayew pulled another back after the break Leicester repelled a late rally to claim all three points.
Rejuvenated under Shakespeare following Claudio Ranieri's sacking last month, the first half was once again a throwback to last season's flying Foxes.
West Ham simply could not cope with the pace and before they knew it the hosts were 2-0 down.
In the fifth minute Mahrez swung in a cross towards Vardy and Shinji Okazaki, but both forwards missed it -- as did West Ham's defence -- as the ball flew into the corner of the net.
Two minutes later, from a Leicester free kick, Marc Albrighton clipped the ball into the box with the outside of his boot and the unmarked Huth nodded in the second.
West Ham were dealt another blow after a quarter of an hour when captain Winston Reid went down clutching his leg and had to be replaced.
But they grabbed a lifeline in the 20th minute after Michail Antonio was fouled by Danny Drinkwater and Lanzini curled in a superb 20-yard free kick.
Ayew and Michail Antonio fired wide and Andy Carroll had a goal ruled out, correctly, for offside as West Ham sensed they could haul themselves back into the game.
However, Vardy restored Leicester's two-goal lead before half-time when he pounced on the loose ball after West Ham failed to clear Albrighton's corner.
Vardy could have added a fourth after the break when he raced on to Mahrez's through-ball and lobbed Darren Randolph, only to clear the crossbar as well.
Instead West Ham pulled another back after Kasper Schmeichel got a hand to a Lanzini free kick which was not on target, and instantly regretted it as from the corner Carroll's header was turned in by Ayew.
The suddenly re-energised Hammers poured forward but Schmeichel clawed out Carroll's header, Ayew skied a glorious chance and Cheikhou Kouyate's shot was blocked on the line.
And in stoppage time Schmeichel made a stunning point-blank save to deny Carroll as Leicester held out to take another big step away from relegation trouble, and continue to prove there is life in the champions yet.