Striker Luke Moore struck five minutes from time to condemn the Magpies to defeat at the Liberty Stadium.
"We are frustrated and disappointed we did not even get a draw as we more than deserved that. We sat off them for the first 20 minutes of the first half but we sorted that at half-time," he told reporters.
"The goal was sloppy, it's a ball into the box, we had four defenders there and it should have been dealt with better; unfortunately it wasn't and it cost us."
The defeat leaves Newcastle in 15th place in the Premier League.