Millwall's all-time record goalscorer Neil Harris came off the substitutes' bench to give the Lions a 1-0 first-leg advantage in their Coca-Cola League One play-off semi-final with Leeds.
Harris, who had not scored since March, made the most of a rare lapse from Richard Naylor to smash home his 117th goal for the club, having been a first-half replacement for the injured Jason Price.
History would certainly favour a Leeds win over two legs - they have won all three of their previous semi-final clashes, while the Lions have qualified for the play-offs four times before and never progressed to a final.
But the Londoners will head to West Yorkshire for Thursday's second leg hoping that counts for nothing as they seek promotion to the Championship after three seasons back in the third tier.
It was the visitors who had the first sight of goal in just the second minute when top scorer Jermaine Beckford expertly held off Zak Whitbread to get on the end of a hopeful knock forward by Naylor, and his shot from the edge of the box forced a save from David Forde.
The Lions then saw on-loan Price hobble off, completing a miserable week for the 32-year-old, who was released by parent club Doncaster on Thursday.
The final ball was lacking from both sides, so Harris took to carving out his own chance, beating Ben Parker and cutting inside, but his shot was well blocked.
A brilliant block from Whitbread prevented Beckford from opening the scoring early in the second half after a smart interchange with Luciano Becchio.
Sam Sodje then did well to prevent Whitbread getting on the end of a James Henry free-kick, before Casper Ankergren was called into action for the first time, diving superbly to his right to keep out Harris' instinctive flick from six yards out.
But the deadlock was broken 20 minutes from time, when Gary Alexander raced on to a long ball and crossed into the box, where Naylor missed it and Harris controlled and saw off the challenge of Jonathan Douglas before firing into the bottom corner, sparking a mini-pitch invasion.
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