The decisive goal came in the 63rd minute when Tomer Hemed played in Gross on the left flank and he then cut inside and hit an effort which was too powerful for Heurelho Gomes to stop.
Brighton should have had more
The home side should have won by a much bigger margin. Hemed had a couple of chances that he missed. Centre halves Connor Goldson and Lewis Dunk both went close from corners and Anthony Knockaert also went close a couple of times. If they had been more clinical we could have been talking five or maybe six nil.
Unfortunately though, The Seagulls let a few chances go amiss but luckily didn't rue them when Gross finally slotted one into the goal.
A fantastic first half
Albion came out and from the sixth minute were all over the visitors. They finished the half with two shots on target and a couple off target. They also picked up a few corners and really went at Watford.
But again, if Brighton were much more clinical they would have gone in with a well deserved lead at the break.
The whole starting eleven played excellently for Brighton
You could not fault a player out there today for Brighton. Goldson made a great first start to his Premier League career. Gross and Hemed worked tirelessly upfront to hassle the defence and create a number of chances and also make good runs in behind the defence.
Davy Propper and Dale Stephens bossed the midfield battle making numerous interceptions and seeming to have a lot of time on the ball.
Knockaert, Bruno and Markus Suttner all looked very menacing down the wing and put some good deliveries into the box.
Both Goldson and Dunk looked very comfortable and composed at the back and Andre Gray failed to cause any threat to them in the air or on the floor.
Watford looked poor
Watford looked very poor defensively and going forward apart from on the counter. They struggled to find any rhythm going forward.
The only player of note that turned up for the visitors was Richarlison. The winger caused The Seagulls a couple of problems but not regularly enough to worry The Seagulls too much.
Apart from that Watford were very poor. Gray struggled against the two big physical centre halves of Dunk and Goldson.
While at the back the defence struggled against the pressure that Hemed, Gross, Knockaert and Solly March put on them and this led to Hemed and co making some runs in behind them on a number of occasions.
What's next for both sides?
Brighton now head into a tough Boxing Day trip away to Stamford Bridge and Champions, Chelsea who only managed a draw away at Everton this weekend.
Watford will be looking to bounce when they entertain Leicester City at Vicarage Road, who play Manchester United later tonight in what will be a very tricky game for them.