Yannick Bolasie headed home his first Boro goal as Neil Warnock's side battled for a point with Watford.
The Championship's in-form side had taken the lead with a deflected effort in the first half, while Boro lost Sam Morsy to injury.
But Bolasie ensured the Teessiders took something from the game, heading in from Paddy McNair's free-kick.
