"Competition for places is vitally important to any side. You could see against Bolton how the substitutes - Antoine Sibierski, Danny Tiatto and Richard Dunne - all lifted us when they came on and that is what competition for places does."
City's convincing win over their local rivals came without any contribution from internationals such as Paul Bosvelt, Trevor Sinclair and Berkovic.
"They know that they have to perform when they get the chance or someone else will come in and do so. I left Paul Bosvelt out because he had had a real tough game in midweek in Lokeren and ran a million miles for us on a tacky pitch. Trevor Sinclair declared himself fit but hadn't trained because of a dead leg since Lokeren.
"The reason I have a big squad here is so that I don't have to ask Trevor Sinclair to go out there maybe be 90 or 95 per cent fit," Keegan added. "He was able to have a rest and get himself for the three very tough away games that face us next week."
One will certainly get their chance while Shaun Wright-Phillips serves his three match suspension after Saturday's red card.