Floored by Yaya Toure's winner for Manchester City in the FA Cup semi-final at Wembley on Saturday and with their treble bid in tatters, United have had minimal time to recover.
However, van der Sar knows that as they head up to the north-east, United need to adopt a positive frame of mind, and he is confident they will.
"It won't be difficult to pick ourselves up," he said.
"We know how important the league is. We are in first position, so we just have to make the best of it.
"We were a little bit tired (on Saturday). The pace of our game was not quick enough.
"We have played a big number of games in the last three or four weeks and against Newcastle we must do better."
After a draining and disappointing day, United could not have hoped for a better outcome to Sunday's game at the Emirates.
They now know 13 points from their last six games will be enough to claim the title for a record 19th time.
It could be less than that too, as United still have their two closest rivals to play at the start of next month, Chelsea heading to Old Trafford on May 8, seven days after the Red Devils have visited the Emirates.
Neither game will hold any fears, particularly if United can get the setback against City straight out of their system.
Sir Alex Ferguson's team have an excellent record at St James' Park and prior to Saturday's defeat they had won six matches on the trot.
"It is always nicer when you find form straight away," added van der Sar.
"We were a bit scrappy in the first half of the season and conceded some last-minute goals that cost us a few points.
"When things like that happen, it doesn't do your self-confidence a lot of good.
"It shows the strength of character and the belief this manager has in the quality of his team that we were able to come through those moments."
Van der Sar insists the overall mood is still good at United as the season enters its crucial final weeks.
"You get confidence when you get on a roll," said the Dutchman.
"When you are not struggling and you get your players back it is bound to make everyone feel better about themselves.
"There are goals in the team too and defensively we are sound.
"No one likes to lose at any time but in general, there is a good feeling about how things are going."