United lost at home to City in the Manchester derby last Saturday and subsequently left the Netherlands empty-handed following a 0-1 defeat to Feyenoord Rotterdam in the Europa League group stage contest on Thursday.
Shaw was rested for the trip to Rotterdam but is raring to go for this weekend's clash at Vicarage Road and he's urging the Reds to be quick off the block.
"We need to start the game sharp. The last two games we've played, we haven't made the best of starts especially in the first half, and we need to change that," Shaw told United's official website.
"It was frustrating to watch (against Feyenoord). We didn't have many chances against us and their goal was a clear offside -- we were unfortunate with that. We created a couple of chances, not many, but the ones we had were quite clear. We were unlucky not to score," he added.
"Both games are gone now and we need to look forward. We need to focus on ourselves and how we start (on Sunday). We need to get off to a quick start and hopefully get an early goal that would settle us."
United have won their last six Premier League fixtures against Watford but the former face a side that ended a three-match winless run with a two-goal come-from-behind 4-2 victory over West Ham United.
United head coach Jose Mourinho, who is expected to put out his strongest XI after making as many as eight changes in Rotterdam, acknowledged it won't be easy to bounce back from consecutive defeats.
"I don't think it will be easy (to bounce back) but the game will be independent. It is a new event, it is another match, it starts at minute zero and so I think it has nothing to do with the two previous matches," Mourinho said.
"Obviously when you lose matches then the mood and feeling is not the same. That is normal, but we are experienced people and the players are very good guys. I know they want to win, they want to work and that is what we have to do."
