The Red Devils entered the break down 3-0 in the Carabao Cup semi-final first leg at Old Trafford.
Marcus Rashford pulled one back for the hosts in the second-half, but Solskjaer was still reeling about the opening stanza when speaking after the game.
"From their goal until half-time it's the worst we've played," he told a news conference.
"Before then, it could've gone either way, a goal, but that doesn't matter now.
"We've just got to focus on Saturday, Norwich [City]. After that second half we've got something that we can believe in."