The Baggies were beaten 2-0 at the Stadium of Light to make it three defeats in their past four outings but it was more the manner of how the team was beaten rather than the result for a dissatisfied Mel.
"I'm very disappointed, particularly with the first half," he told Sky Sports.
"Sunderland defeated us in terms of intensity, in terms of winning the second balls and going into tackles strongly.
"I believe that we weren't as convincing.
"It was a case of putting out fresh players, players who hadn't played as much, but the result wasn't much of a good one."
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