The Black Cats were beaten 2-1 by the Latics on Saturday, with that scoreline doing little to reflect the visitors' dominance.
The result leaves Ricky Sbragia's men within three points of the Premier League trapdoor with only nine games remaining in which to secure their safety.
While things are starting to look bleak on Wearside, Whitehead believes Sunderland have enough to beat the drop providing they continue to focus on the challenges to come and do not concern themselves with the failings of the past.
The 27-year-old said: "I don't think it was must-win for us - there are a lot of teams in worse positions than us.
"But we have to take this on the chin and move on now.
"It was one of those days and we have to put it behind us and make sure we are focused on the next game at Manchester City."
FlatWhitehead admits the weekend performance against Wigan was not good enough, especially as the Premier League is such an unforgiving division.
"It was a flat day. We didn't get going from the start and we paid the price," he said.
"We weren't quite at it from the start, we weren't at it all over the pitch and our shape was all over the place.
"They have got good players and we were punished.
"If there are five, six, seven players not at it, you are not going to win games in the Premier League."