A sloppy second half effectively handed the Hornets three gift-wrapped points at Vicarage Road thanks to two penalty blunders from Matt Ritchie and Javier Manquillo.
United have another quick turnaround for their next game as they face Spurs at St James' Park.
Bruce was not entirely dissatisfied with his side's performance and said at his Press conference: "It is important we finish the season off now.
"We could have gone 2-0 up when Allan Saint-Maximin burst through and hit their goalkeeper.
"They then needed a shot in the arm.
"I then felt the only way they could beat us was set-pieces.
"To give them two penalties is naive or they were really soft, I will let others make that judgement."
He added: "We needed a response from the other night (0-5 at Man City) and I thought the first half performance was very, very good.
"The second half performance gave them a huge lifeline.
"Whether it was a penalty - with VAR and it (decisions) supposed to be clear and obvious - I will let other people make their mind up.
"They looked remarkably soft to me."