Preston wanted a win to climb into the play-off places and instead remain seventh with just one win in their last six matches.
Watford remain 12th – three points outside the top six – and Still can take heart from his side’s point at Deepdale.
Preston took advantage of some slack defending to open the scoring on 19 minutes when Imran Louza failed to track back and Benjamin Whiteman fired in a low cross for Dobbin to sidefoot home his eighth goal of the season at the far post.
The Hornets levelled on 55 minutes out of nowhere when Louza broke and fed Maamma, who cut inside and curled the ball into the far corner.
And two minutes later, they went ahead when Nampalys Mendy found Kwadwo Baah and his cross for Luca Kjerrumgaard went in off the unfortunate Offiah.
Heckingbottom made changes and two of his substitutes combined to haul them level on 70 minutes when Lang, on debut, played a fantastic ball into Osmajic, who buried his shot in the bottom left-hand corner.