There were just 90 seconds on the clock when the stand off, trying to impress onlooking GB coach Brian Noble, struck a 35 yard effort to nudge Warrington in front for the first time in the game, handing them their first ever play-off victory.
Briers kicked a penalty right on the hooter to reduce the deficit to 12-6, and it was reduced further when Michael Sullivan grabbed a try at the start of the second half, as Warrington started to turn the screw.
Leeds released the pressure through 2 Kevin Sinfield penalty goals, giving them a 16-10 lead, but when Ben Westwood dived on Lee Briers' kick through for a third Wolves try, which was converted by Briers, the visitors were back on level terms.
Sinfield edged Leeds in front on 67 minutes with a one-pointer only for Briers to duly reply 2 minutes later.
But as the fans and media were beginning to contemplate golden point extra time, Briers held his nerve and secured a stunning win for the visitors, and surely staked his claim for a place in Great Britain's Tri Nations squad this winter.
"We have been hardened by our season's adversity. We held our nerve and I thought that was evident tonight.
"We have played out an entire season in 80 minutes. It very much reflects our season. It was an honest effort and I'm proud of the way the club responded."
Cullen's opposite number Tony Smith could only contemplate on what might have been as his side's season ended prematurely. "In the first half we pretty well dominated most areas but in the second half we played the game at the wrong end.
"They've got some opportunists in their team who came up with big plays.
"I thought we got out-wrestled tonight. They're playing different rules now. There were no penalties given in the ruck area. The only penalties were for high shots."