O'Sullivan watched in admiration on Saturday as Scotland produced a gutsy display against the world champions without ever coming close to gaining their first Calcutta Cup win since 2000.
Such is the strength of Sir Clive Woodward's squad, nobody will be predicting a first Irish triumph at fortress Twickenham for a decade when the teams meet on March 6 even though O'Sullivan's side completed their own impressive demolition job on Wales on Sunday.
But O'Sullivan is calling for his team to reproduce the whole-hearted endeavour Scotland showed at Murrayfield, which, allied to Ireland's extra class, should ensure England are at least given a hard time.
"Scotland were outmuscled at times on Saturday, but they made England work for the whole 80 minutes and that is the key," he said
"The most important thing is to make them earn their victory. They are the world champions and a class side, but if they are not quite on their game, that is when you can get at them.
"Scotland didn't shirk from the battle - and that is what we will have to do in two weeks' time."
O'Sullivan will not expect Ireland to dominate in the forwards as comprehensively as they did against Wales. But he will have gained enough encouragement from his team's elusive back play to recognise if they can gain parity in possession, they could put England under a lot of strain.
The Irish coach admitted it had been a gamble to pair Brian O'Driscoll in the centres with Gordon D'Arcy.
And if D'Arcy, who plays his provincial rugby for Leinster on the wing, had not been forced off with severe bruising to his back, the margin of yesterday's 36-15 triumph could have been a lot wider.
"Brian and Gordon are very similar as players," reflected O'Sullivan.
"They are quite elusive, but can also distribute. From a defensive point of view, it makes it very difficult to play against them because if you try to shut them down, they can still offload."
D'Arcy is expected to be fit to face England, although abrasive lock Donnacha O'Callaghan is not likely to be so fortunate after damaging medial knee ligaments.