Barnet and Swindon Town will be level going into their Johnstone's Paint Trophy southern area final second leg following their Underhill draw.
The hosts lost Danny Senda to a suspected broken leg in the first half.
The Robins led when Aden Flint scored with a header from Paul Caddis's corner just before half-time.
But the Bees rescued a draw when Mark Marshall's quickly taken free-kick caught Swindon's defence out and Mark Hughes nodded home.
The second leg will be on Tuesday, 7 February, with the winners to take on Chesterfield or Oldham in the Wembley final.
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Swindon Town manager Paolo di Canio told BBC Wiltshire:
"We were up 1-0 and we deserved to stay at 1-0 but then we conceded a stupid free-kick.
"In some ways I am happy as it's not easy to find the energy as we spent a lot, mentally and physically, in the last game.
"It's the first time we have finished looking a bit tired."