The Black Cats lost crucial ground in the race for automatic promotion after their 1-1 draw at the Posh on Easter Monday.
Max Power thought he had handed Sunderland an important victory at London Road when he fired home on 87 minutes.
However, Peterborough’s Matt Godden popped up in injury-time to score a dramatic late leveller and maintain Darren Ferguson’s side’s hopes of making the League One play-offs.
The draw leaves the Wearsiders fourth – two points adrift of Pompey and four behind second-placed Barnsley.
Both the Blues and Sunderland have played a game less than the Tykes.
However, the initiative has swung Pompey’s way following their latest win against Coventry – and it’s they who have their destiny in their own hands ahead a mouthwatering finale to the season.
A home win is also a must if Sunderland are to maintain their hopes of a top-two finish.
And Ross is confident his side can get over their Peterborough setback in time to get their automatic promotion hopes back on track against Pompey.
Following the draw at Peterborough, Ross told the Black Cats’ official website: ‘It’s (the changing room) quiet and everyone is frustrated having put so much into the game.
‘To get yourself ahead so late on and then concede in the manner we did is really frustrating and a hard one to take.
‘We have put a lot into this season and we want to get our rewards for it.
‘At this stage, we have two choices. We can either feel sorry for ourselves or we can regroup and go again.
‘The lads will be ready to go on Saturday because we have got another big game.
‘We came into this block of five games looking to win every single one.
‘We knew if we did that then it would take us to where we wanted.
‘Unfortunately, we’ve dropped two on the road and now it’s been taken out of our hands. All we can do is win our remaining three and see where it takes us.’