The Baggies face the Toon this weekend.
"I went up to watch Newcastle at the weekend and it was a great atmosphere and a really good performance by Sunderland," Clarke told the WBA website.
"Derby games are different, they are one-offs.
"I think they maybe got Newcastle at a good time, when they had just been knocked out of the Europa League, and, as Alan Pardew said, there was maybe a little bit of tiredness mentally and physically.
"They have had a fresh week this week and I'm sure they will be fired up to get the win they need to cement their position in the Premier League for next season."