The Hornets began brightly at Vicarage Road but nearly conceded after just three minutes played from a dangerous free kick 30 yards out.
The Hornets sprung to life after the Cherries' effort and went on to take the lead on 13 minutes through Kiko Femenia, who volleyed an inswinging corner kick into the back of the net from 14 yards out via a Steve Cook deflection.
Eddie Howe's side matched their opponents during the first half and were given the opportunity to level when Jose Holebas was adjudged to have handled the ball in the box, and Joshua King duly rolled home the resulting penalty.
However, Javi Gracia's charges were ahead once again not long after the restart, Troy Deeney's delivery into the box resulting in the ball being worked to Roberto Pereyra, whose low shot took a slight deflection before trickling into the far corner.
Both sides continued to trade blows during the second half but, just as it seemed like the Hornets were home and dry, Bournemouth struck for a share of the spoils.
A free kick was flicked on by Ake beyond the napping defence and into the path of Defoe, who had time to let the ball bounce before hooking past the onrushing Karnezis from 10 yards out.
WATFORD (4-2-3-1): Karnezis; Janmaat, Mariappa, Prodl (Cathcart 64'), Holebas; Capoue, Doucoure; Kiko (Richarlison 81'), Hughes (Okaka 76'), Pereyra; Deeney
BOURNEMOUTH (4-4-1-1): Begovic; Fraser, S. Cook, Ake, Daniels; Stanislas (Pugh 45+3'), L. Cook, Gosling, Ibe (Defoe 67'); King; Wilson (Surman 81')