Wednesday, under caretaker manager Stuart Gray, registered their biggest Yorkshire derby win against Leeds with a thrashing to maintain their climb up the Sky Bet Championship table.
First-half goals from Reda Johnson and Atdhe Nuhiu put Wednesday firmly in control and, after Leeds substitute Matt Smith had been sent off two minutes into the second period, Connor Wickham added a killer third.
Chris Maguire's deflected free-kick in the 67th minute and substitute Caolan Lavery's superb late double ensured Leeds slumped to their heaviest defeat of the season and not since a 4-0 victory in October 1955 have Wednesday enjoyed such a comfortable win against their White Rose rivals.
While Wednesday were impressive, Leeds somehow managed to plumb new depths after last week's 2-0 FA Cup defeat at Rochdale.
Whites boss McDermott said the cup loss was the low point in his managerial career, but Saturday's defeat at Hillsborough plunged the former Reading manager deeper into despair.
He will call all his players in on Sunday for a clear-the-air meeting after a fourth straight defeat dealt a huge blow to his play-off aspirations.
When asked if he could take any positives from his side's display, McDermott said: "Are you serious?
"After that, in a local derby, it's public humiliation as far as I'm concerned.
"It has to start on Sunday morning and I'll go back to basics with this team to do whatever we've got to do as a group.
"That was just unbelievable. It doesn't matter about being lower than the Rochdale game, that's just humiliating for all of us.
"I don't distance myself from the players because I'm part of the group. We've had a good run to get to 35 points, but we're having a poor time now.
"It's a terrible time for Leeds United, the supporters and us."
McDermott added that he was considering appealing against Smith's dismissal by referee Lee Probert.