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."

South Africa's instruction was that the money was for a Diaspora Legacy Programme which should be "implemented directly" by Mr Warner, Fifa said.
The US says the $10m was a bribe in exchange for Mr Warner supporting South Africa's 2010 World Cup bid.
Mr Warner and South African officials have denied any wrong doing.
South Africa won the bid ahead of Morocco to become the first African country to host the World Cup.
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Mr Warner hails from Trinidad and Tobago and was the president of the Confederation of North, Central American and Caribbean Association Football (Concacaf) and vice-president of Fifa when the decision was made.
He was among a string of Fifa officials arrested last week after the US and Switzerland launched separate investigations into corruption in Fifa, the world football governing body.
In a statement, Fifa said South Africa's government approved a $10m project in 2007 to "support the African Diaspora in Caribbean countries as part of the World Cup legacy".
The government, in agreement with the South African Football Association (Safa), asked Fifa to "process the project's funding by withholding" $10m from the Local Organising Committee (LOC) of the World Cup, the statement added.
"Fifa did not incur any costs as a result of South Africa's request because the funds belonged to the LOC. Both the LOC and Safa adhered to the necessary formalities for the budgetary amendment," it said.
Martyn Ziegler, chief sports reporter for the Press Association, has tweeted a 2008 letter from Safa to Fifa secretary general Jerome Valcke, who has denied involvement in the scandal.
The letter, written by then Safa president Molefi Oliphant, requests that the money should be sent to the Diaspora Legacy Programme to be "administered and implemented directly by the president of Concacaf".
A Fifa spokesman told the BBC in response to the letter that the football governing body wanted to reiterate that Mr Valcke and other members of its senior management were not "involved in the initiation, approval and implementation of the diaspora project".
The Fifa statement did not comment on another US allegation - that a senior South African official travelled to Paris to hand over cash in $10,000 stacks - in a hotel room, to an unnamed person working for Mr Warner.
South Africa's government and Safa have denied any bribes were paid.
Mirco Antenucci's second-half strike saw Uwe Rosler's Leeds rescue a point against his old club Brentford.
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Fifa says it paid $10m (£6.5m) to a Caribbean football body led by Jack Warner, who is charged by the US with corruption, at South Africa's request.