The Hornets had led 1-0 and looked to be on their way to upsetting the formbook against the home side, who were unbeaten in 11 games before today.
It was Laken Torres who gave Watford the lead after only nine minutes when he turned sharply in the box and sent a rising shot past Cherries keeper Cam Plain.
Soon after the Hornets came close to extending their advantage when Plain got down well to block a long-range Jake Watkiss effort.
Towards the end of the first half Watford came even closer to a second goal when Aidan Coyne saw his volley crash back off the bar.
Early in the second period Plain went full-length to push away a fiercely-struck effort from Junior Gyamfi.
Just past the hour mark Jonathan Macaulay preserved Watford’s lead when he pushed away a ferocious drive from Dominic Sadi before preventing Balraj Landa from converting the loose ball.
However, in the 77th minute, the home side equalised. Substitute Kian Tydeman squared for Finn Tonks to drive the ball past Macaulay.
Watford’s hopes of emerging with a point ended eight minutes from the end when Tydeman and Sadi exchanged passes before setting up Dan Adu-Adjei to score from close range.
The victory leaves Bournemouth second in the Premier League Development League South table, a point behind leaders QPR, while Watford stay seventh.
Watford: Macaulay; Gould, Trialist, Coyne, Mullins, Abbot, Adu-Poku, Davis, Torres, Gyamfi, Watkiss. Subs: Browne, Eames, Taylor, Hamiga, Holding