The game was effectively over inside the opening 20 minutes as Boro conceded three goals thanks to some calamitous defending.
Adrian Mariappa's own goal reduced the arrears with 11 minutes left, but the Teessiders are still to pick up their first Championship away win of the season.
David Wheater was at fault for their first concession, with his shocking backpass enabling former Boro striker Danny Graham to open the scoring after just 17 seconds. Wheater did not look around as he rolled the ball behind him, and instead of finding Jason Steele, he found the feet of Graham, who calmly did the rest.
Watford were two up inside 11 minutes, with Jordan Mutch hammering home a 20-yard half-volley after Barry Robson could only half-clear a corner from the right.
And the hosts had a third nine minutes later as Graham claimed his second of the game. Don Cowie skipped past Matthew Bates on the left flank, and Chester-le-Street-born Graham rolled home the winger's cut back from the edge of the six-yard box.
Boro's only first-half effort saw Andy Halliday direct a weak header well wide of the target, but the visitors should have clawed a goal back five minutes after the break.
Gary O'Neil was all alone at the back post as Robson crossed from the left, but the midfielder directed his shot straight at the legs of Watford keeper Scott Loach.
Boro finally clawed a goal back with 11 minutes left, but they needed a Hornets defender to score it for them.
Loach saved well from Scott McDonald, and as the ball looped back into the air, Mariappa headed it into his own net under pressure from Kris Boyd.
WATFORD (4-4-2): Loach; Hodson, Mariappa, M Taylor, Doyley; Buckley (McGinn 65), Eustace, Mutch, Cowie; Graham (Walker 86), Sordell (Deeney 77).
Subs (not used): Gilmartin (gk), Bryan, Whichelow, Oshodi.
MIDDLESBROUGH (4-5-1): Steele; Bates (McMahon 55), Wheater, McManus, Arca; McDonald, O'Neil, Tavares, Robson, Halliday (Boyd 46); Lita (Kink 66).
Subs (not used): Coyne (gk), Hines, Bailey, L Williams.
Source: Northern Echo
Source: Northern Echo