Boro were relegated from the top flight in 2009 and have taken their time to rally a serious promotion challenge but this could be their year after goals from Lee Tomlin, Kike and Albert Adomah sealed their place at Wembley.
Meanwhile, Brentford ended a fantastic season with a whimper as manager Mark Warburton oversaw his last match in charge as he is leaving in the summer after a messy fallout with owner Matthew Benham.
The Riverside Stadium was bouncing at kick-off as the sell-out crowd rekindled the spirit of the famous European nights under Steve McClaren in 2006.
Boro went into battle without the Championship’s Player of the Year though with Patrick Bamford only fit enough for the bench after failing to recover from an ankle injury.
A few eyebrows were raised that the 18-goal forward wasn’t risked, but that was soon forgotten as Boro put in a commanding performance from the first kick.
Captain Grant Leadbitter and Adam Clayton provided the foundations for their side to control proceedings and they took the lead on 23 minutes.
Clayton played a fantastic 40-yard cross-field pass into the feet of Adomah, who jinked inside and found Tomlin on the edge of the area. Boro’s creative chief looked up and perfectly curled the ball into the top corner via a slight deflection off Brentford defender Harlee Dean.
Brentford’s response was limited but Andre Gray should have done better just before half-time when presented with a free header eight yards from goal, but he fluffed his lines.
Warburton’s last half-time team talk as Bees boss was perhaps the most important of his career but his words didn’t render the desired effect as Kike doubled the lead on 55 minutes.
Tomlin again was at the heart of the move, releasing Jelle Vossen through on goal. He couldn’t quite muster a clear goalscoring opportunity but the ball broke to Kike eight yards from goal and he stepped inside and smashed the ball into the roof of the net.
Boro were now cruising with Brentford struggling to break through the two-man wall of Clayton and Leadbitter in the heart of the midfield.
A third goal always looked likely on the break and it came on 76 minutes through Adomah, who was a constant source of imagination on the right wing.
He played a lovely one-two with Tomlin inside the box and showed real class inside the area to shift the ball away from the goalkeeper and fire into the net via the underside of the bar.
It was Premier League quality from Boro. They are now just 90 minutes away from the promised land.
Middlesbrough: Konstantopoulos (7), Friend (7), Ayala (7), Whitehead (7), Gibson (7), Adomah (8), Clayton (8), Leadbitter (8), Kike (7), Vossen (7), Tomlin (8).
Subs: Woodgate (6), Reach (6), Forshaw (6)
Brentford: Button (6), Bidwell (5), Dean (6), Tarkowski (6), Odubajo (7), Jota (5), Douglas (5), Judge (6), Diagouraga (5), Gray (5), Pritchard (6).
Subs: Toral (6), Long (6), Dallas (6)
Man of the Match: Albert Adomah