Evans' early header set West Brom on its way to halting a 20-game run stretching back to August, with fellow defender Craig Dawson heading in at the start of the second half.
West Brom made the best possible start at The Hawthorns as Evans, who continues to be linked with Manchester City and Arsenal in the January transfer window, scored after just four minutes. Matt Phillips' driven cross from a corner was flicked on by Jay Rodriguez and Evans headed the ball in at the far post.
Another driven corner, this time from Chris Brunt, was met at the far post by Dawson and his 55th-minute header into the ground bounced up and over Anthony Knockaert on the goal-line and in.
It was Alan Pardew's first league victory since he took over as manager nine matches ago at the start of December. But the Baggies remained in the relegation zone with tough games against Manchester City and Chelsea coming up in the next month.
Brighton is just three points clear of the bottom three after a sixth successive goalless game away from home - a run which includes five defeats.
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