Adrian Lam admitted Wigan's attitude wasn't good enough after their 23-22 loss to Hull FC in golden-point.
Oliver Gildart's late, unconverted try had given the Warriors hope they could snatch victory at the DW Stadium in sudden-death extra time - the first Super League game to be settled by the new rule.
But Mark Sneyd struck a decisive drop-goal, before the hosts had even had possession, to claim FC's first win since last June.
And disappointed coach Lam admits they ultimately paid the price for a flat start which saw them trail 16-6 at one stage in the first-half.
"We started flat and were flat throughout the whole game," he said. "We battled back but there were not good signs at all through the whole match.
"It was another slow start, we included a few new faces to try and freshen it up but we couldn't get out of second gear.
"If Hull had been on they could have hurt us a bit more than they did. We were all over the shop defensively.
"I felt our atttitude was down a bit, were weren't really true to our values at the club."
Lam, who handed debuts to Liam Byrne and Australian Jarrod Sammut, said there were no warning signs of the lacklustre display from the way they dusted themselves down after the World Club Challenge loss a week earlier.
"We trained well so I didn't see that coming," he said. "We're a good training team."
Ben Flower left the action with a rolled ankle which isn't thought to be serious, and Joe Greenwood will need to pass a concussion assessment before next week's game at London Broncos.