United were already 2-0 up through first-half goals from Martha Thomas and Alessia Russo when Zelem’s 60th-minute corner evaded everyone in the penalty area and nestled in the far corner.
And the 26-year-old, who also scored from a corner in the FA Cup last weekend, amazingly repeated the feat a few minutes later to set the seal on a comprehensive win.
The victory lifts Marc Skinner’s side to third in the table, six points behind leaders Arsenal, who take on bottom side Birmingham on Sunday.
The visitors had the ball in the net after eight minutes when Kayleigh Green headed Megan Connolly’s free-kick beyond Hannah Hampton, only for the goal to be disallowed for a marginal offside.
But there was no doubt about what proved to be the winner in the 28th minute as Le Tissier swept home a superb half-volley from Connolly’s corner.
Brighton moved up to sixth in the table on 22 points, with Villa remaining ninth on 16 points.