The 25-year-old winger stood with his hands on his head on the pitch at the Stadium of Light on Boxing Day after his England international team-mate had hurled himself across goal in an attempt to keep out his dipping left-foot strike.
Hart got to the ball after initially appearing to be wrong-footed, but several seconds elapsed before it became clear that he had been unable to prevent it from creeping under him and into the bottom corner to spark belated celebrations by Johnson and his team-mates.
The Sunderland man said: "I know Harty is probably the best keeper in the world and I have seen him many a time save those.
"I thought he had saved it and it had gone under him and around the side of the post, not in the net. I couldn't see the ball because he was covering it.
"But obviously when the crowd cheered, I knew it was in and that's when I realised. It all happened so quickly."
- Sports & Recreation