After a tight first half, the turning point in the match came on the stroke of half-time when Hoops striker Georgios Samaras was adjudged to have been brought down in the area by Langfield, who was shown a straight red card.
Kris Commons made no mistake with his penalty before Celtic sealed victory through James Forrest's fortuitous effort, which looped off Mark Reynolds and over replacement keeper Nicky Weaver's head from a tight angle.
McInnes said on BT Sport 2: "I was disappointed that Samaras gets the chance to go through on goal but the referee called it right. There was definite contact there, the referee's made the right decision.
"There wasn't a lot in the game first half and I thought we could get something from the game but at 10 men in the second half there was only one team in it.
"They're a good team and they had a element of control, 11 against 10.
"The second goal was freakish, you'll never see another goal like it this season.
"I think 2-0 was hard on us but we'll pick ourselves up."
Celtic boss Neil Lennon concurred with McInnes' assessment of the penalty decision and subsequent sending off.
"I thought it was clear penalty. The goalkeeper's unfortunate, it's the law and it's very very tough at times," he said.
Celtic striker Forrest, who came off the bench to seal the win for his side, admitted the Hoops were given a stern test at Pittodrie against one of the sides predicted to challenge them in the league this season.
"It was a hard game, we knew coming here it was going to be," he said.
"I think there's a few tough games and Aberdeen away is definitely up there (with one of the toughest games of the season)."