Duff scored in the 4-1 FA Cup win over the Potters ... along with Owen, Cacapa and Milner ... when KK was named new Toon manager.
The 29-year-old, clearly feeling the benefit of a rare injury-free pre-season, was in sparkling form against the Monkey Hangers, and was rewarded with a well-taken hat-trick.
Keegan: "There's absolutely no doubt of that. The lad has never had a pre-season for three years.
"He is at the weight he was when he was 18 and he has worked so hard in training, the running and the way he has worked with everything we have put on probably showed out there on Saturday.
"After 70, 80 minutes, he still looked like he had got a turbo-charger in him, as did James Milner and a couple of the others.
"You have just got a draw a line under where he has been and just judge him from now, now he has had a chance to put a foundation into his season, which he hasn't had for three years.
"Any players who misses the pre-season, you ask any player, no matter how good they are, where they have played and what qualities they possess, it is very hard without that base.
"I think you will see a different Damien Duff this season. There were signs of that on Saturday, but obviously, there is more to come.
"There has been speculation about every one of our players, but I definitely want to keep him.
"He is a good character around the place, he sets a good standard in training along with three or four of the other players.
"They set the standards, they are the ones who do it right every day. Rain or sunshine, it doesn't make any difference to them.
"We are very strong now in certain positions. Where Damien plays is where Gutierrez can play, where James Milner can play, where Charles N'Zogbia can play and where Geremi can play.
"We have got five very good players competing for two-and-a-half places in the team.
"We haven't got that everywhere, so we need to address that and that is what we are trying to do.
"It might look like not so successfully at the moment, but there is a long time to go and there will be plenty of opportunities.
"If the right player comes along and we think he is right for Newcastle United, we will be in there pitching."