Millwall took a giant stride towards Championship safety with a 3-1 win over Cardiff City at the Den.
Michael Obafemi had put the hosts ahead on eight minutes but Cardiff levelled through Yakou Meite.
Jake Cooper smashed home in first-half stoppage time before Duncan Watmore tapped home late on to seal the win for Millwall.
The victory for the Lions puts them six points clear of the Championship bottom three and surely safe this season.
Millwall's shock victory against Leicester City undid the damage of defeats to relegation rivals Rotherham and Huddersfield.
Lions boss Neil Harris made one change from the win over the Foxes, with Romain Esse replacing the injured George Honeyman.
Cardiff were without the injured Aaron Ramsey, while defender Mahlon Romeo and forward Callum Robinson were left out for a second successive match after what boss Erol Bulut described as a "disciplinary penalty".
Harris, who was meeting Cardiff for the first time since his spell as manager of the Welsh club finished, came into this contest with his side still looking anxiously over their shoulders at the bottom three.
A fast start for the hosts seemed inevitable with the stakes high and Millwall delivered as they tore into Cardiff, playing at a tempo the visitors struggled to contain.
Millwall took the lead on nine minutes as former Swansea striker Obafemi pounced after Zian Flemming's lofted pass undid Cardiff, with Obafemi racing clear and firing into the corner of the net.
The hosts were the better side and Ryan Longman tested Ethan Horvath before Cardiff equalised with a set-piece routine as Meite headed home from Rubin Colwill's sweet delivery with goalkeeper Matija Sarkic beaten at his near post.
Millwall were rattled by Cardiff's leveller and Nat Phillips could have put the Bluebirds in front, but he missed the target from 12 yards out.
The miss proved pivotal as Millwall went ahead in first-half stoppage time as Cooper blasted home from close-range after Longman flicked on Esse's cross.
Both sides had chances to score after the interval with Horvath getting down smartly to tip behind Obafemi's effort, while Sarkik saved well from Joe Ralls' long-range shot that he saw late.
Millwall were largely able to contain Cardiff, however, and they scored a third with a fast break in stoppage time as substitute Watmore converted from Brooke Norton-Cuffy's cross.
Millwall have now won four of their last five league games against Cardiff City.
Millwall: Šarkić, McNamara, Cooper, Tanganga, Mitchell, Fleming, Longman (Norton-Cuffy 84'), Flemming (De Norre 90+5'), Obafemi (Bradshaw 71'), Saville, Esse (Watmore 46').
Subs Not Used: Białkowski, Hutchinson, Nisbet, Mayor, Bryan.
Cardiff City: Horvath, Ng, Goutas, Phillips, Collins, Ralls (Turnbull 69'), Siopis (Wintle 60'), R.Colwill (Tanner 74'), Grant, Bowler (Ashford 69'), Méïté (Diédhiou 60').
Subs Not Used: Turner, Conte, Sawyers, J.Colwill