Jonny Evans and Craig Dawson netted past Socceroos goalkeeper Ryan to give the second-bottom Baggies their first league win since August.
As things stand on the point tally, Chelsea are now on level terms with second-placed Manchester United with the Devils yet to play a game. If Conte is unable to motivate his players then we have very little chance of progressing in the competition.
Currently, Chelsea rely heavily on one system to beat teams - their 3-5-2.
Three 0-0 draws in as many games marks what has been a very frustrating week for Chelsea.
Mahrez thought he had should have had a 55th-minute penalty after he tangled with Andreas Christensen, on for the injured Gary Cahill, although referee Mike Jones seemed to have made the right call to turn down the Algerian's appeal.
He said taking off Cesc Fabregas and Eden Hazard was an easy decision: "I saw they were were very, very exhausted".
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"Then when I chose to put fresh energy on, the game changed".
Antonio Conte has hit out at Chelsea for failing to deliver his main transfer targets.
They were soon given a major boost for the final 20 minutes as Leicester were reduced to 10-men, as the impressive Chilwell was given his marching orders for two yellow cards in the space of five minutes, his second for a late challenge on Victor Moses.
OVER AT THE JOHN SMITH'S STADIUM: Marko Arnautovic created three and scored the other as West Ham lifted themselves away from the Premier League relegation zone with a 4-1 victory over Huddersfield Town.
Watford 2-2 Southampton Abdoulaye Doucoure's controversial last-gasp equaliser denied Southampton a first win in 10 matches.
Just two goals in eight Premier League games, Morata's poor form continued against Leicester. Speaking ahead of today's game against Leicester at Stamford Bridge, Morata said: "It's hard to get something here (for opposition teams) and between now and the end of the season we need to win even more games at our home".