The Tigers endured a miserable afternoon at The New Den as Kenny Jackett's side ran riot with two goals from Steve Morison and further strikes from Kevin Lisbie and Liam Trotter.
Pearson had no complaints about the result and urged his players to move on quickly from the disappointment of dropping out of the Premier League.
Pearson said: "I think I've got to just take that on the chin. There were some things today that were very frustrating but I'm not going to take anything away from Millwall. I thought they were excellent.
"I've seen all the goals and there's certain passages of play I'm very disappointed with but its something we'll put right.
"To give yourself a chance of getting anything out of any game then you need to do the basics right and we didn't. I'm a realist and I know there's a lot of work to be done here.
"If there's a hangover from last season then we need to get over that quickly and put it behind us. But the fashion of the defeat was the most disappointing thing for us."
Millwall: Forde, Dunne, Robinson, Ward, Barron, Henry, Trotter, Abdou, Schofield (Hackett 86), Morison (Harris 82), Lisbie (Carter 79). Unused substitutes: Mildenhall, Mkandawire, Smith, Marquis.
Hull: Duke, Solano (McShane 36), Zayatte, Anthony Gardner, Dawson, Atkinson (Koren 46), Cairney, Ashbee, Kilbane, Bostock, Garcia (Cullen 46). Unused substitutes: Oxley, Cooper, Devitt, Cousin.
Referee: A Penn (W Midlands).
Man of the match: Robert Koren.