Derek Adams thought his side were 'scared' of the occasion in the first half at the Stadium of Light.
Sunderland ran out comfortable 2-0 winners on Saturday afternoon, a scoreline that could have been far heavier had the home side taking greater advantage of their superiority in the opening 45.
Plymouth improved in the second half, with Adams believing his side should have had a penalty when Tom Flanagan blocked a shot from Gary Sawyer inside the box.
Adams felt Flanagan had handballed, but was critical of the way his team started the game.
"In the first half we didn’t press Sunderland enough," he said.
"It looked like we were scared today, being perfectly honest.
“I think the occasion got to too many of the players today. Their ball retention was poor and their choice of passing actually was poor as well.
“We changed it when Kyle went down injured in the first half and got a better grip of the game.
"We forced the players then to play forward and take chances, and with that we created a few opportunities.
"The second-half was a lot better and we should have had a penalty for handball which, at 1-0, could have been crucial."
Plymouth brought almost 2,000 fans to Wearside but Adams thought the occasion got to them.
"Some of them are not used to playing in front of 30,000 people, and that's not an easy thing to overcome," he said.
"Today we weren't able, especially in the first half, to cope with that. I thought we were a lot better in the second half."