Leicester dropped two crucial points in their quest for Premier League glory after they could only manage a 2-2 draw at home to West Brom.
The Foxes are three points clear of second-placed Tottenham, who go to West Ham tonight, where they could go top on goal difference.
Goals from midfield duo Danny Drinkwater and Andy King cancelled out Salomon Rondon's early opener before Craig Gardner's classy free-kick earned a point for Albion.
Jamie Vardy and Shinji Okazaki hit the bar for the hosts, who were the better side for much of the game, and Wes Morgan blew a glorious chance to win it late on.
Claudio Ranieri's side will now face an anxious wait when Spurs go to Upton Park.
The Foxes' pre-match points tally of 56 was already their highest ever in the top flight but cracks showed despite their late 1-0 weekend win over Norwich.
Elsewhere, Norwich's luck deserted them once again as Diego Costa scored from an offside position as Chelsea won 2-1 at Carrow Road.
Bournemouth beat south coast rivals Southampton 2-0 in an uninspiring match at Dean Court with the victory keeping the home side eight points clear of the Premier League relegation zone.