Mark Warkburton warned Middlesbrough they may have celebrated prematurely after Brentford were beaten 2-1 in the first leg of their Sky Bet Championship play-off semi-final.
Substitute Fernando Amorebieta scored a dramatic stoppage-time winner to make it advantage Boro going into next Friday's second leg at the Riverside.
Bees boss Warburton said: "There's a lot of celebrating going on, which is fine, they are 2-1 up at our place. They've gone back with a one-goal advantage - but that's all it is.
"We've been to some tough venues this year and taken the points and we are more than capable of doing that again."
Andre Gray had earlier capitalised on a blunder by Boro goalkeeper Dimi Konstantopoulos to cancel out Jelle Vossen's first-half header.
The clash was the outgoing Warburton's final game in charge at Griffin Park, and his dream of signing off at Wembley is now hanging by a thread.
But he added: "There's no negative thoughts among the players, it's 2-1 at half-time. There's frustration, but there are another 90 minutes to play.
"The crowd were magnificent from the first minute to the last. Griffin Park is a special place under the lights."
The visitors took the lead after 25 minutes when Vossen slipped unnoticed between two Brentford defenders to meet Adam Clayton's cross and guide his header across David Button and into the corner of the net.
Brentford equalised after Konstantopoulos came to meet the ball on the corner of the area, only for Gray to charge down the keeper's clearance before spinning round and slotting the ball into an empty net.
But Amorebieta stunned Griffin Park in the third minute of injury time when George Friend headed down Grant Leadbitter's corner and the full-back's shot clipped Jake Bidwell and flew into the net.
Boro boss Aitor Karanka said: "I'm very pleased, we won the game and have another at home on Friday.
"After this game I'm very pleased because maybe this season we have played well and not scored goals and today we didn't create clear chances and we scored two goals."
Boro had a familiar face rooting for them from the stands in the shape of Jose Mourinho, to whom Karanka was assistant at Real Madrid.
He added: "It's nice when a friend comes to support you. We have a very good relationship after working together for three seasons.
"In the same way I was happy for him last week against Crystal Palace he will be pleased for me."
Source: PA
