A change in personnel and formation offered the U's a chance to try something different in this cup match, and for an hour, they were well in this game.
However, quick fire goals were the U's undoing as Albion stretched their legs in the second half to take the match away from John McGreal's men.
The U's Head Coach will want to get the goals conceded out of their system ahead of a home double against Cambridge and Grimsby this weekend.
The U’s made seven changes to their starting eleven from the game against Hartlepool, which also saw them switch to a 3-5-2 formation against the Seagulls.
The Seagulls started the game on the front foot, though, with Manu and Lua Lua making the most of space down the side of the three centre halves to cause problems.
Both had shots on goal, but the first was blocked and the second hit the side netting as the home side asked the early questions.
The U’s had chances of their own as they started to get a measure of the challenge in front of them and twice Guthrie and Johnstone combined, with the former having two shots blocked after the visitors got up the pitch and around the box.
And whilst the Albion wingers were seeing plenty of the ball, U’s wing back Dickenson embarked on a fine run on 26 minutes that took him past four and it required Ince’s sliding challenge to clear.
The U’s had to remain on their toes, though. Manu was a constant threat and span Kent in the box on the half hour mark, only for the visiting defender to recover and stab clear before the shot was taken.
At the other end, Szmodics’ eyes would have lit up when Dickenson swung over an excellent cross, but he could only head back past the post with Maenpaa flatfooted.
His fellow midfielder Lapslie burst into the box on 32 minutes but the ball was just beyond his diving leg.
Barnes had not had much to do in the opening half hour, but on 34 minutes tipped over a White cross that looked like it might creep in had the U’s keeper left it.
Johnstone nearly capitalised on a defensive slip before running out of room as he got into the box, before Holla had a great chance for Albion, but his dinked effort dropped wide of the post with Barnes scrambling back.
Albion had a chance just before half time, as the ball was cleared as far as Norwood, who whipped one just past Barnes’ left hand post.
It was all square at the break, but Barnes had a nervous moment as he shovelled a ball away from danger in the six yard box from White’s low cross.
The U’s keeper did much better as he hooked clear a cross from the other side of the box by Murphy at the end of a driving run, and Baldock could only lift his shot from the rebound over the bar.
Brighton had started the second half well, but the U’s had a chance just before the hour mark as a darting Szmodics run was ended on the edge of the box,. However, Loft’s free kick was well wide.
The U’s midfielder went into the book four minutes later, tugging back Lua Lua as he embarked on another run through the heart of the pitch.
The visitors could do little about it on 64 minutes though, when Lua Lua took a long ball out of the air and controlled it perfectly, before passing to Baldock.
He took a touch and bent it into the goal beyond the despairing dive of Barnes.
Then the home side extended their advantage in quick fire fashion as the game entered its final quarter. First Lua Lua burst forward and lay it into the path of the bursting run of Murphy, who dinked home.
Then it was three as a low cross from the left was converted at close range by Manu to take the game beyond the U’s.
The U’s had introduced Bonne, Slater and Dunne either side of the third goal, and Dunne had a shot from the edge of the box on 78 minutes that went just past the near post.
Lua Lua and Manu fancied their chances now, but Barnes pulled off two good stops in a double block to stop a further goal being added to the tally.
However, Murphy was the man to add a fourth as he drove forward late on in the game to beat several players, before finishing smartly past the helpless Barnes.
The scoreline was perhaps harsh on the U’s after a good hours work and boss John McGreal will want to eliminate the goals conceded out of his side’s upcoming performances, with two big home games to come.