Pompey had drawn themselves level eight minutes after the restart through Jed Wallace before conceding three goals in eight minutes to see the game slip from their grasp, meaning John Marquis' late strike was a mere consolation.
Whittingham insists he doesn't want a repeat performance from his team as they slipped down the league table.
"It was a poor performance," he blasted. "You can protect people so much if you feel they've given their all but today we didn't give our all. That's the first time it's happened and it's got to be the last time.
"I'm extremely disappointed. You can't do that in any football game. All we ever want to see from our players is that desire - desire to do well and hard work.
"It's not a case of playing well or not playing, it's that desire to work hard and we didn't have that today. I'm extremely surprised by it. We've got to make sure it doesn't happen again.
"It wasn't John Sullivan's best day. We should be talking about Jed Wallace's goal - what a fantastic goal he scored - but unfortunately we're not."
The Minstermen made the perfect start with Wes Fletcher scoring the first of his double early on before further goals from Lewis Montrose and Ryan Jarvis sealed the points.