We go into Easter weekend level on points with Arsenal and battling out for Champions League places with the Gunners, Chelsea and Newcastle, who moved above Chelsea with Friday's win at Swansea.
Sunderland have climbed up to ninth since the arrival of Martin O'Neill in December and impressed with a 3-3 draw at title-chasing Manchester City last week.
The Black Cats led 3-1 until City's late revival but still became the first team to take points off City at the Etihad this season.
"They had a great result at City," said Harry. "It will be a difficult game but we have to keep going.
"We can't afford to drop too many points because Arsenal, Chelsea, Newcastle, they are all right there.
"It will be a dog fight until the end so we have to go up there and make sure we get the right result."
Harry said Sunderland had been 'fantastic' under O'Neill.
"I was impressed with them last year when Steve Bruce was there," he added. "He did a great job there but things didn't turn out for him in the end and he moved on and Martin has come in and as Martin always does, he has got them up and going straight away and has done a great job there."