Mick McCarthy's men looked down and out when Watford scored with a controversial penalty after 67 minutes but their sense of injustice at the referee's decision proved the catalyst for their revival.
"I would not say it was a fortunate point but I could not see it coming when we were two goals down," said McCarthy. "We deserved a point with that fightback but not all three."
Watford boss Ray Lewington cited the fear factor which proved to be his side's undoing.
"The finishing line was in sight but then we gave away a really sloppy goal to a set-piece and you could see the fear spreading throughout the team.
"In the end we were lucky to get a point because Sunderland should have scored a third and that would have been a disaster."
Watford scored after seven minutes when Gavin Mahon picked his spot after good work by Scott Fitzgerald set him up with a clear chance.
Mahon, Sean Dyche and particularly Neil Cox should have added to the score as Watford counter-attacked effectively.
Martin Poom saved two of the attempts, but should have been beaten when Cox, unmarked some eight yards out, headed over.
Poom saved well to deny Neal Ardley early in the second half, but then a tackle by Phil Babb on Heidar Helguson which appeared to be just outside the box enabled Cox to fire Watford into a 2-0 lead.
But in the 76th minute substitute Marcus Stewart pulled a goal back from a corner and then Darry Byfield, who signed 24 hours earlier, celebrated his debut by turning and hitting the equaliser after 86 minutes.
It could have been worse for Watford, but Jason McAteer, looking certain to score, sent the ball against the upright and Watford scrambled clear in the final moments.