Timlin, whose sickening clash of heads with Stevenage skipper Bira Dembele overshadowed Sunday’s 1-1 first-leg draw, fittingly scored the extra-time goal which secured a 3-1 win and a place in the League Two play-off final.
A surprise inclusion in the starting line-up and wearing Petr Cech-style headgear after needing 15 stitches in a gaping wound above his eye, Timlin played the full 120 minutes and rounded off a courageous display by racing through to wrap up the victory.
And Shrimpers boss Brown said: “For Michael Timlin to get that goal…dear me!
“It emphasised the commitment that was shown to try to win the game. We never do things easy at this place – it doesn’t seem that way anyway.
“I have made some big decisions in my life football-wise and that’s probably the biggest, Michael Timlin to play.
“On Sunday he went in for that horrific challenge and their captain’s laid out. In the 90th minute here he went into another header with a skullcap on – it was just the bravest performance I’ve seen from an individual in my managerial time.”
The Shrimpers had finished 12 points clear of their opponents but still made hard work of booking their trip to Wembley against a dogged Boro side.
They fell behind to Tom Pett’s close-range 55th-minute strike and, after Ryan Leonard had equalised, Barry Corr blew the chance to send Southend through when he missed a stoppage-time penalty.
But sub Stephen McLaughlin nodded them in front 18 minutes into extra time and Timlin added the gloss at the death to send Brown back to the scene of his memorable promotion to the Premier League with Hull seven years ago.
For Boro, defeat means another season in the basement division, although manager Graham Westley admits he might not be a part of it.
He said: “They’ll take so much confidence from this and there’s a real chance in that dressing room that they can have a good season next year.
“We will see where things go from here. I am the Stevenage manager up until the end of May.
“There’s been no offer to me. The club is having a serious re-think about what it’s going to do for the future so we’ll see how that pans out.”