Substitute Keith Treacy marked his Burnley debut by scoring a late equaliser to deny Sean Dyche a dream start to his Watford reign.
Rookie boss Dyche, 40, saw his side race into a 2-0 lead through Craig Forsyth and Mark Yeates.
But the Clarets recovered in the final 13 minutes as Charlie Austin pulled a goal back.
And fellow substitute Treacy - a summer signing from Preston - headed an 84th-minute equaliser.
Burnley, led by new skipper Chris McCann in the heart of midfield, made a bright and purposeful start.
They threatened in the fifth minute when midfielder Dean Marney hit a fierce right-foot shot which sailed just wide from 20 yards before Ross Wallace's effort drew a fine block from Adrian Mariappa.
The hosts were firmly in the ascendancy and moments later Jay Rodriguez engineered the space to hit a shot from six yards which missed the target.
But the pendulum swung in Watford's favour when Chris Iwelumo, a summer signing from Burnley, tried his luck from 18 yards with a shot that home debutant Ben Mee did well to block.
And Watford opened the scoring on the stroke of half-time when Marvin Sordell flighted a right wing cross for Forsyth to head into the bottom corner from six yards.
Burnley made a tactical switch at half-time as Martin Paterson was replaced by Austin in a bid to boost the home attack.
Yet Watford continued to defend strongly as Austin wasted a decent opening before Forsyth shot wide when well placed.
Yeates was denied by a smart stop from home keeper Lee Grant on 54 minutes and his endeavour was rewarded in the 70th minute when he drilled home a right-footed shot from 12 yards.
However, the Clarets responded in the 77th minute when Austin fired home from six yards and, with six minutes remaining, Treacy nodded in a cross from fellow wideman Wallace to level the scores.
Burnley 01 Grant 02 Trippier 03 Fox 21 Amougou Booked 36 Mee 06 McCann 07 Wallace 08 Marney 11 Elliott (Treacy - 64' ) 09 Rodriguez 10 Paterson (Austin - 46' ) Substitutes 12 Jensen 15 Edgar 20 Bartley 26 Treacy 23 Austin Watford 01 Loach 03 Dickinson 05 Taylor 06 Mariappa 12 Doyley Booked 04 Eustace 07 Yeates 11 Forsyth 14 Jenkins 10 Iwelumo (Deeney - 68' ) 20 Sordell Substitutes 13 Gilmartin 21 Mirfin 23 Mingoia 09 Deeney 27 Massey