McInnes said: "It wasn't quality that beat us and I mean that with all due respect to Celtic.
"They have loads of quality players and they are here because they are winners and more determined, more than anything.
"It was their determination to get the ball over the line which ended up beating us."
McGinn claimed Forster's save was "maybe a turning point" in the game.
"If that had gone in, it would maybe have been a different story," the Northern Irishman said.
"But fair play to Fraser, it was a great save, he just tipped it onto the post.
"Sometimes they go in, sometimes they don't. But I don't think that was the be all and end all.
"We gave away two late goals which was the disappointing thing."
- Sports & Recreation
- Fraser Forster
- Niall McGinn
- Kris Commons
- Georgios Samaras