Deeney says the Hornets fully deserved their 3-1 Premier League victory.
He told BT Sport: "It is nice for us to get back-to-back wins. We have had the toughest start of any club.
"To come out with seven points is massive for a club like us.
"I am not surprised by how we played. We should take a bit more credit, we pressed well, condensed the space and were tough in the tackle.
"We need to be against teams like Manchester United who have high quality players and spend a lot of money.
"We have some really good quality players and men in there, which is the hardest part, I thought we were the better side and had a lot of chances, even when they scored we showed what we are made of and came again."