The Greece international's 54th-minute strike was of stunning quality, but in stark contrast to much of what either side produced during a largely dour 90 minutes with clear-cut chances at a premium.
Boro created the better of what few opportunities there were and saw four penalty appeals rejected by referee Roger East, some of them with greater merit than others.
TWEET OF THE MATCH
"A fairly moribund game comes to vivid life with a fine strike from Holebas" - The Times chief football writer Henry Winter.
In an ordinary contest, few players excelled and the quality of Watford wing-back Jose Holebas' decisive goal was a rare oasis in the desert
He will not catch many sweeter than that one.
MOMENT OF THE MATCH
Middlesbrough keeper Victor Valdes had been a virtual spectator for much of the opening 54 minutes, but he found himself picking the ball out of the net when Holebas unleashed a fierce strike from distance after running on to Marten de Roon's clearance.
Boro's Alvaro Negredo powered a 28th-minute header just over the angle of bar and post, but was relieved rather than disappointed
The striker was back inside his own penalty area and came perilously close to converting Holebas' free-kick in some style.
Victor Valdes 5
Antonio Barragan 5
Calum Chambers 6
Ben Gibson 7
George Friend (Capt) 6
Marten de Roon 5
Adam Forshaw 6
Cristhian Stuani 5
Gaston Ramirez 7
Stewart Downing 7
Alvaro Negredo 6
Adama Traore (for Stuani, 69 mins) 6
Daniel Ayala (for Barragan, 69 mins) 6
Jordan Rhodes (for De Roon, 89 mins) 6
Heurelho Gomes 6
Nordin Amrabat 5
Younes Kaboul 6
Sebastian Prodl 6
Miguel Britos 6
Jose Holebas 7
Etienne Capoue 6
Valon Behrami 5
Isaac Success 6
Roberto Pereyra 6
Troy Deeney (Capt) 5
Juan Zuniga (for Amrabat, 72 mins) 6
Christian Kabasele (for Britos, 85 mins) 6
Ben Watson (for Success, 88 mins) 6
WHO'S UP NEXT?
Arsenal v Middlesbrough (Premier League, Saturday, October 22)
Swansea v Watford (Premier League, Saturday, October 22)
Source : PA