The Blues last night suffered a deeply-disappointing 3-1 defeat at the leaders in front of the television cameras.
The visitors were second best during a contest in which Rovers emphatically emphasised their promotion credentials, completing the double over Pompey in the process.
It ensures Darren Ferguson’s side are now 10 points ahead of the Blues as they continue to set the pace in the promotion race.
Having played 48 hours ahead of this weekend’s fixture list, Cook’s men remain four points adrift of third spot – and firmly involved in the battle.
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However, Doncaster continue to surge on, last night marking 13 league matches at home without defeat this season.
Not that Cook has conceded defeat in pursuit of a club firmly on target to make an instant return to League Two.
He said: ‘You never know, we could catch them.
‘We’ve all seen what happens when you win games, you have a strong week and win Saturday-Tuesday-Saturday to get nine points.
‘Meanwhile, someone else draws two and loses one and you are all over them.
‘Darren has done a great job at Doncaster.
‘They were relegated last year after 17 games without a win, that is what football is like.
‘They are well-organised, have a good, strong team and I wish them well but I am not giving up on catching them.
‘They are in a strong position but what we have got to do is make sure we look after ourselves.
‘We have done well recently, it was just disappointing last night and like everyone else I wasn’t happy.’
– NEIL ALLEN