David Moyes labelled the late defeat to West Ham as “harsh” on his side as the Black Cats were downed by a last-gasp goal.
Winston Reid bagged a contested 94th-minute winner as Sunderland's first visit to the Hammers' new home ended on a sour note.
The Black Cats were just seconds away from a point and clean sheet before Reid struck, leaving Moyes to rue what might have been.
“It was a very harsh way to lose a game,” said the Scot, whose side host Arsenal on Wearside next week.
“I was pleased with a lot of what the players did today. It was always going to be a tough game – West Ham have some good players.
“We struggled for the first 20 to 30 minutes, but after that we did quite well and created some chances ourselves.
“We're very disappointed to lose the game.”
He added: “I've looked at the goal back and I've confirmed to the referee that we believe it was offside. The referee believes it was not offside.
“I thought we competed and did quite well. We are disappointed, the players worked so hard and we've dropped a point in the end.
“We had some big chances to score ourselves and we wanted to build some confidence.”