The Seagulls began the game on the front foot and Inigo Calderon lined up an effort from the edge of the box but his strike was blocked. He and his teammates appealed for handball against Cian Bolger, but the referee dismissed their claims for a penalty.
Brighton continued to threaten the Southend goal as Danny Holla lined up a free kick from the edge of the box, successfully curling his effort over the wall but Daniel Bentley managed to make the stop.
Southend came into the game as David Worrall was allowed to raid down the left flank and he cut back onto his right foot, but his curling effort went inches past the post.
After the break, Worrall caused problems for the visitors again as he drove an effort at goal from the edge of the box, but his strike went just wide of the target.
Gaeten Bong carved out an opening for the visitors when he raided in from the left wing and curled a strike with his right foot towards goal, but it went narrowly wide of the target.
Southend should have taken the lead as John White lifted the ball to the back post for the run of Ryan Leonard, but he put his header past the post.
The match looked to be heading for extra time until Holla threaded a pass through behind the Southend defence for the run of LuaLua, and the forward maintained his composure to fire the ball past Bentley.