Bees debutant Marco Djuricin had given his side the lead when he found the net with a curling strike.
And the Austria international almost doubled his tally after the break when his first-time shot clipped the post.
But, after Chris Wood saw his attempt turned onto the woodwork at the other end, substitute Antenucci dispossessed Ryan Woods before firing in to level.
Leeds have now scored just twice against Brentford in five matches, having failed to win any of the games dating back to the 2009-10 season.
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The visitors took the lead when Djuricin, who joined on loan from Red Bull Salzburg on 31 August, found the net midway through the first half.
Jake Bidwell then went close to doubling the lead when his second-half header bounced across goal, before another Djuricic attempt hit the post.
Leeds striker Wood also saw a deflected effort hit the woodwork, when his shot was turned onto the post by Bees goalkeeper David Button.
But, just when it looked like it might turn out to be a first defeat of the season for the hosts, Brentford's debutant substitute Woods - who had only been on the pitch for two minutes - was easily dispossessed by Antenucci and the Italian, who had come on at half-time, fired home the equaliser into the corner with his left foot.
The result means Leeds remain unbeaten this season, having drawn five of their six opening games in the Championship.
Leeds manager Uwe Rosler:
"We lost our fearlessness and we made a mistake. When you do that against Brentford they can find the holes.
"Then we were down on confidence and they scored. We looked like we were afraid to get on the ball, that can happen. We deserved to trail at half-time.
"In the second half we started 0-0 and the substitutes helped us. The last 25-30 minutes we battered them in a football sense and could have won the game. I think it was a fair result for two teams who wanted to win."
Mirco Antenucci's second-half strike saw Uwe Rosler's Leeds rescue a point against his old club Brentford.