The Wearside club were beaten 3-0 by the Toffees at the Stadium of Light after Romelu Lukaku ran riot with a second-half hat-trick.
The performance, particularly in the second lot of 45 minutes, was simply not good enough from the Black Cats and young winger Watmore wants better for the supporters.
"We've got to go again for the fans because that wasn't good enough in that second half today," he told Sky Sports.
"The goals are frustrating. The manager's annoyed. I'm trying to be positive but we've got to go again
"We need to get the fans behind us and make sure they keep cheering us because it wasn't good enough again today."