It was total domination from the Premier League champions in the early proceedings, with good chances from Rhiyad Mahrez and Slimani before the Algerian striker gave them the lead 20 minutes in. Good opportunities from Demari Gray and Michail Antonio followed, but the score remained the same.
The Hammers came into their own in the second period with good opportunities for Andy Carroll and Aaron Cresswell but the Foxes held out for their first win in four.
Domination from the off
The Premier League champions had been struggling for the past few weeks, but looked a different side when they came out against Slaven Bilic’s men.
Darren Randolph was called into action only two minutes in when Mahrez’s hit a dipping volley from Gray’s lofted ball, but the goalkeeper did brilliantly to keep out the Algerian’s effort.
They came even closer two minutes later, when Marc Albrighton broke down the right before floating it towards the back post. Silmani was there but the angle was against him as it came off the post.
It was only a matter of time before the Foxes took the lead, and Silmani who managed to draw first blood 20 minutes in. Albrighton did well to capitalise Dimitri Payet’s defensive error and whip the ball in, and Slimani was on the end of it to head back across Randolph and into the net.
Starting to get into it
After falling behind, it seemed to kick the Hammers into life as they looked to get back into the contest. Before that it could have easily been two for Claudio Ranieri’s side, as Gray’s dangerous ball took a flick of Angelo Ogbonna which forced Randolph into a good reaction save to keep it at one.
West Ham’s first real opportunity came just four minutes from the break, as Antonio did well to turn and get his shot off but it came crashing off the crossbar.
Tale of two halves
Ranieri's side came out for the second period with contrasting intensity to that of the first period, and that allowed the Hammers into game for some decent half opportunities.
The first came in the 58th minute when substitute Manuel Lanzini did well to pick out Carroll, who lined up the effort but Robert Huth got across brilliantly to deflect away any danger.
The next came ten minutes later as Cresswell lined up a free-kick, it was low from the full-back and Kasper Schmeichel did well to block the effort.
A late flourish
Bilic's side continued to push for the crucial equaliser as the clocked ticked down, but it was the Foxes who had a late flourish as they looked to wrap up the game in the final moments.
Havard Nordtveit had done well in the 90th minute to block Leonardo Ulloa's effort at the back post, but the defence continued to be bombarded. The ball made its way to Benjamin Chilwell with his effort blocked by Randolph, before Shinji Okzaki headed the rebound onto the roof of the net.
West Ham had one last throw of the dice in extra-time as Ogbonna threw himself into the header, but Daniel Amartey did well to throw his body into the path of the seemingly goal-bound effort.