Keane said: "It was a bad piece of defending for the penalty. (Niko) Kranjcar is clever and experienced and our lad (Phil Bardsley) stuck his foot out.
"But we never looked like scoring. David James can never have had an easier game in his career.
"Maybe one or two of my players were overawed by one or two Pompey players. You shouldn't be collecting players' autographs.
"We've lost far too many games too easily and although it was a referee's decision again today we can't be victims all the time."
Keane was clearly upset by Sunderland's eventual surrender after they had cocooned disappointing Pompey in a midfield trap for the first hour.
Defoe stepped up to rifle in a penalty, his second goal in successive home games since a £7.5million move from Tottenham, after Kranjcar, cutting in from the left, kept his feet when stumbling over a challenge by Andy Reid then went down over Bardsley's outstretched foot.
Pompey boss Harry Redknapp said: "Niko wouldn't go down (deliberately). He never likes going down, he doesn't want to get his knees dirty.
"The referee seemed to have no doubt it was a penalty and I thought so too - although I haven't seen a replay yet.
"I was delighted with the result because the game was just as tough as I expected. They outnumbered us in midfield with their 4-5-1 and made it hard for us.
"We can't really play 4-4-2 because our wide players Kranjcar and John Utaka haven't got a defensive bone in their bodies but Sol Campbell and Sylvain Distin were comfortable at the back and when I put Niko out wide in the second half he caused problems there.