The Premier League side face their third replay in the competition after being held by Championship side West Bromwich Albion.
Albion were full value for a replay after twice coming back from behind and this was a proud return to his home club for West Brom manager and former Boro hero Tony Mowbray.
Mowbray was given a warm reception before the kick-off by fans who remembered his influential role in a double promotion triumph after a liquidation crisis 20 years ago.
Mowbray could be proud of the performance of his promotion challenging side and on the evidence of this game Middlesbrough will have their work cut out in the replay.
Boro went ahead after 33 minutes after Julio Arca. Stewart Downing provided a right-wing cross to Arca who was in a perfect position to head into the net from close range at the far post.
The Albion fought back to level before the break through Diomansy Kamara, who was the visitors' outstanding player.
The goal was an embarrassment for Australia international Mark Schwarzer. The goalkeeper was a hero with a double penalty save in the fourth round replay win over Bristol City, but on this occasion he allowed the ball to go through his legs.
Just before the break the home side regained their lead when Albion skipper Curtis Davies brought down Yakubu in the box.
Yakubu had missed two penalties in the Bristol City replay but showed tremendous bottle to have another go. He gave Dean Kiely no chance with his eighth goal in the last nine home games.
West Brom went all out for an equaliser after the break and were rewarded when Kevin Phillips equalised with a deflected shot from a Paul Robinson pass.
Middlesbrough skipper George Boateng struggled in midfield as the Albion stepped up the tempo and there was no question of the visitors adopting a closed-shop policy to earn a replay.
The Midlands side looked determined to record their fifth successive away win.
There was plenty of action in the free-flowing game but ironically neither goalkeeper had a lot to do.
Emanuel Pogatetz headed wide for Middlesbrough who were second best after the break.
West Brom lost skipper Davies in the final minutes when he was sent off for a second bookable offence, with the two sides left to try again at The Hawthorns a week on Tuesday.