Salomon Rondon, back in the Magpies' starting XI after being on the bench at Liverpool, hustled the Hornets' defence all day and his first-half header had appeared enough to have the visitors on course to three valuable points in their fight for Premier League survival.
But Watford, who made six changes from their Boxing Day defeat to Chelsea, roused Vicarage Road as substitute Doucoure headed them level with eight minutes remaining to seal a 1-1 draw.
Watford enjoyed plenty of early possession with Paul Dummett doing well to prevent Gerard Deulofeu getting a shot off as he slid in to block following a superb flicked pass from Will Hughes.
The former Barcelona winger did test Martin Dubravka shortly afterwards, with the Newcastle goalkeeper equal to his strike.
Benitez's side, as they have so often this season, set out defensively and rarely threatened in the opening exchanges – but they still hit the front before the half-hour mark.
Christian Atsu rolled the ball out to Matt Ritchie, whose deep cross was powerfully headed home by Rondon, who climbed above Adam Masina to clinch his fifth goal from his last eight Premier League appearances.
The Venezuela international turned in again five minutes before the break, only to see an offside flag rightfully result in the finish being ruled out.
Isaac Success stung the palms of Dubravka as the hosts chased an equaliser before the break following a tepid first-half performance from the Hornets.
It looked as though that leveller would come courtesy of Success, only for Federico Fernandez to make a last-gasp block behind.
With just eight minutes of the second-half played, Gracia turned to captain Deeney and Doucoure in an attempt to get his side back into the contest.
Although Deeney added a physical presence, Watford were still struggling to create clear chances as Newcastle adopted a counter-attacking approach, which saw Ritchie test Ben Foster with 20 minutes remaining.
Five minutes later and Deeney finally forced Dubravka into a save, but it was simple for the Slovakia international to keep out a tame downward header.
Watford would come up with their equaliser but it was Doucoure and not Deeney who powered home a header, turning Deulofeu's pinpoint cross home.
Success struck straight at Dubravka in stoppage time as the hosts unsurprisingly were the side chasing the late win – but both teams had to settle for a share of the spoils.