O'Driscoll was convinced Dean Shiels should have been credited with a winner at Vicarage Road, and insisted video evidence supported his claim.
Shiels thought he had scored just before the hour mark when he met Gareth Roberts' flick following a corner, however referee Neil Swarbrick decided that a fine save from England Under-21 goalkeeper Scott Loach had stopped his shot on the line.
"We've got a tape of the game and it's clearly over the line," said O'Driscoll.
"It's a difficult one to give. The linesman was 40 yards away and the referee's in line with it, but until you get cameras on the goalline it's one of those that you've got to take on the chin.
"I don't think you can blame anybody. I don't think anybody can actually see. I don't think even our players would be, if they're honest, totally sure.
"I don't think we can hark on about it. I think it would be a bit churlish to blame a linesman who is 40 yards away and a referee who's got a million and one other things to look at.
"I think he's in the right position to see what's going on in the box, but, unfortunately, not in the right position to see if the ball's gone over the line."
Watford manager Malky Mackay played the incident down and said: "I've not managed to get a look at it yet, so I don't know."
Commenting on the game itself, O'Driscoll said: "Two sides worked hard without much quality. I'm sure Malky would say the same. I think we can both play a lot better than we showed. (There were) difficult conditions, it was extremely hot, and the game was in fits and starts throughout the 90 minutes."
Mackay, who had to watch the game in the stands as a result of a two-game touchline ban carried over from last season, remarked: "I was pleased with the effort in the second half. They went out and were really positive.
"It was a very hot day and you're playing against a team who try to keep the ball and like to keep the ball.
"What I asked them to do in the second half was really press them and go out them and push forward and I was delighted with the effort in the second half and the way that with five, 10 minutes to go we were still pressing and pushing on. I think that's testament to the five weeks of pre-season that we did."
Watford took the lead in the 27th minute when the Doncaster defence failed to clear a Don Cowie free-kick from just outside the left of the penalty area.
The ball ran through to last season's top scorer Tommy Smith and his scuffed cross-shot fell perfectly for new boy Danny Graham to tap home from two yards out and start repaying the £200,000 initial payment a Football League tribunal ruled his transfer from Carlisle will cost the Hornets.
But the visitors were back on terms 11 minutes later with a fine effort.
There appeared to be no danger when Brian Stock clipped a ball towards the edge of the area from the left, but James Hayter got in front of Lloyd Doyley to send a looping header over Loach from 16 yards.