Leicester suffered a wobble in their bid for an instant return to the Premier League after a stunning Ryan Longman strike condemned them to a 1-0 defeat at struggling Millwall.
Back-to-back wins had reignited the Foxes’ promotion bid and lifted them back to the top of the Championship.
But they slipped up in south London as the Lions, in need of the points for different reasons, battled to a first win in five matches to go four points clear of the relegation zone.
In a huge match at both ends of the table, Leicester’s defeat will have been welcomed by Ipswich and Leeds as the three-horse race for automatic promotion enters the final straight.
Millwall had a chance to open the scoring in the first minute, George Honeyman floating in a free-kick which Longman headed too close to Foxes goalkeeper Mads Hermansen.
Leicester quickly settled, though, and Stephy Mavididi – the late matchwinner against Birmingham on Saturday – should have done better when he was sent through by Yunus Akgun but his touch was too heavy.
Ricardo Pereira’s clever flick then found Kiernan Dewsbury-Hall, who slipped in Jamie Vardy.
But the 37-year-old former England striker was losing his balance as he got his shot away and Matija Sarkic made a comfortable save.
Dewsbury-Hall, playing as a number 10, took aim from 20 yards but his effort was deflected wide.
Millwall, happy to sit back and let Leicester have the ball, almost snatched the lead on the break before half-time.
Ryan Leonard whipped in a cross from the right and captain Jake Hooper got a firm head on the ball, but it was pushed away by Hermansen.
The goal arrived on the hour and, for Millwall fans at least, it was well worth the wait.
Wout Faes lost the ball in midfield and Billy Mitchell sent Longman scampering away down the left.
The on-loan Hull winger cut inside Harry Winks before curling a spectacular 25-yard effort past Hermansen and in off the underside of the crossbar.
Millwall almost doubled their lead when Michael Obafemi bulldozed his way into a shooting position but Hermansen got down well to save.
Leicester pushed for an equaliser and Pereira got in behind only to see his angled drive blocked by the legs of Sarkic.
They came agonisngly close in stoppage time but were denied by a goal-line clearance from Mitchell to keep out substitute Kelechi Iheanacho’s header.
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