The Red Devils succumbed to a 2-0 defeat against a Watford side that had won just one out of their first 17 Premier League games this season.
The defeat at Vicarage Road means Manchester United have now accumulated 25 points from 18 games, their worst ever start to a Premier League season.
Solskjaer was speaking to Sky Sports after the game, and the Norwegian was not happy with what he saw, especially in the first half.
"We started the game slow,” the former Cardiff City and Molde Fk manager said.
“The first half was very, very poor from both sides and when you concede two goals like we did in quick succession with their two shots on target we gave ourselves too much to do.”
"We had been doing well but you have to earn every single point in this league. It was too slow, it was like a testimonial in the first half from both teams."
David De Gea failed to grasp on to Ismaila Sarr’s effort, which handed the hosts their first goal five minutes after the break.
He added: "It was a mistake, it happens in football and it is what we train for every day to make sure they don't happen again. David has been very good lately, it is just one of those things that happen.”
"You have to earn every point on the pitch and today we didn't deserve that. I can talk about it all day long. We have to face the fact we have two games coming up that we have to improve on."
"We need a reaction,” he concluded.
