Goals from Seb Larsson and Craig Gardner lifted Blues above the injury-hit Black Cats.
Blues have now taken seven points from three games after recovering from the hangover of their Carling Cup triumph over Arsenal in February.
"We lost five or six players after the final through injury and when that happens, it becomes tough," he said.
"The expectancy levels were there because of the cup win.
"Mentally, we suffered after that triumph with a lot of players not used to winning trophies.
"The players have regrouped and we have got some experienced bodies back.
"This was a big win for us."