Manuel Pellegrini's side have now lost eight of their last ten games in the Premier League, and despite some pre-season optimism, the Hammers have a relegation battle on their hands.
Story of the match
The first chance of the game fell to the away side within the opening minutes, Marc Albrighton testing Lukasz Fabianski following the ‘keeper’s return from injury, however last season’s Hammer of the Year saved comfortably.
The Polish international was involved again minutes later, this time for all the wrong reasons after bringing down Kelechi Iheanacho as the forward closed in on goal, conceding a penalty 10 minutes into his first game following a three-month absence.
However, Fabianski continued to steal the show as he saved Demarai Gray’s spot-kick to keep the scores level, the entire stadium taking a breath following a whirlwind start to the game.
The missed penalty ignited the atmosphere with both teams feeding off the noise inside the London Stadium, the home side harrying the Leicester players in possession as the frenetic tempo of the game continued.
Arthur Masuaku forced a good save from Kasper Schmeichel with a strike from distance on 22 minutes, but it was the away team who looked most likely to open the scoring, maintaining pressure and going close on several occasions.
The Foxes did eventually take the lead shortly before the break, Kelechi Iheanacho heading home from close-range after Ayoze Perez nodded back across goal.
It didn’t take long for West Ham to respond though as Pablo Fornals swept home Felipe Anderson’s cut-back to notch his first Premier League goal, 1-1 the scoreline after an entertaining first-half.
Leicester started the second half on the front foot, much like the first, and their first opportunity was presented to Chrstian Fuchs, the set-piece specialist with a free-kick in a dangerous area, but unable to find the back of the net with his driven shot.
Manuel Pellegrini made the game's first substitution after 54 minutes when he introduced Michail Antonio off the bench, but the home supporters were aggrieved by the manager's decision to take off talisman Sebastien Haller with the team in need of three points.
Moments after the change, a blistering counter-attack saw Gray restore the visitors' lead, the speedy winger curling into the far corner after he was played through by Perez.
The goal seemed to deflate the Hammers and the Foxes took total control, pressing for a third and almost finding it through Wes Morgan, Fabianski on hand again to keep his team in the game.
Leicester brought on Wilfred Ndidi and James Maddison as they looked to secure all three points, and as the clock ticked on, the hosts looked devoid of confidence and out of ideas to find a way back into the match.
There were a lack of chances for either side in the final 20 minutes, and the away fans began to cheer every pass as their team kept possession and eased to victory.
Takeaways
Pellegrini under pressure
With another defeat, the pressure continues to mount on manager Manuel Pellegrini.
The Hammers have now lost four Premier League home fixtures in a row for the first time since January 2006, and it remains to be seen whether the Chilean will be in the dugout by the time West Ham face fellow relegation battlers Bournemouth on New Year's day.
Rodgers' rotation pays dividends
With the fixtures coming thick and fast over the festive period, both managers opted to rotate their teams, Brendan Rodgers making 9 changes and Manuel Pellegrini making 7.
Leicester's squad depth proved to be superior as their second-string team was good enough to secure three points, Jamie Vardy left out of the squad completely after his wife gave birth to their third child.
Fornals off the mark
Pablo Fornals got a deserved first Premier League goal to cap off another impressive performance in Claret and Blue.
The Spaniard faced some criticism after taking time to adjust following his summer arrival from Villareal, however the midfield playmaker has picked up a couple of assists in recent games, and was one of West Ham's few bright sparks against Leicester.