Middlesbrough have been dominant in the first 45 minutes against Watford but a resolute Hornets rearguard were rewarded when the visitors took the lead just before the break.
Tony Mowbray's side controlled possession from the outset in a meeting between playoff contenders but have failed to turn their advantage into goals.
Scott McDonald has come closest to breaking the deadlock, forcing Manuel Almunia to make a pair of smart saves with shots on target.
Joel Ekstrand produced a strong last-ditch tackle to deny Lukas Jutkiewicz a free strike on goal from close range.
Gianfranco Zola's side held firm and took the lead with their first shot on target when Matej Vydra took advantage of an error from Rhys Williams to slot home.
