The Hornets, needing the win that would lift them on to 40 points and all but guarantee safety, were on the back foot throughout, carving out few real chances.
They finally pulled one back, with only four minutes left, after a dazzling, tricky run from sub Ikechi Anya.
He went to the byline and perfectly picked out Troy Deeney, whose header denied Jack Butland his clean sheet and gave the home fans false hope of a grandstand finale.
Watford boss Quique Sanchez Flores insists the Hornets are still not safe after only two wins in 13 and nine points out of the last 39.
He said: “We are fighting against this feeling that we are comfortable and have been for some weeks because it’s not true.
“We are not worried about the future in the Premier League but we want to achieve 40 points as soon as possible.”