The Gills search for an away win continues as Mark Stimson's men slump to a 0-2 defeat at the Withdean Stadium.
Stimson altered his formation bringing Garry Richards in to a five man defence while Dennis Oli dropped to the subs bench.
Gillingham made a nervous start to proceedings and were fortunate not to concede in the ninth minute as Bennett's right wing cross deflected on to Royce's near post. Moments later Thornhill let fly from the edge of the box but Royce was able to get a foot on the ball and block a certain goal.
Stimson abandoned his defensive formation, pushing Bentley to right midfield and the switch almost paid off instantly. Barry Fuller's deep ball down the right gave Bentley space to cross and keeper Kuipers had to get down quickly to deny Andy Barcham's low strike.
The home side took the lead in the 24th minute after Adam Miller felled Elliott Bennett on the edge of the box. Miller was shown a yellow card and Bennett dusted himself down before planting a fine effort into Royce's top right corner.
Five minutes later the Seagulls went close again, danger man Bennett swinging a corner to the near post for Glenn Murray which the big centre forward headed narrowly over.
Gillingham's response was a cheeky backheeled effort from Jackson which failed to test Michel Kuipers. As half time approached Miller sent Bentley away on the right, Barcham arrived in time to connect with his low cross but Brighton were able to scramble it clear at the back stick.
Early in the second half Gillingham shuffled their pack again with Oli coming on to partner Jackson in a 4-4-2 and Lewis added to give the midfield a more attacking feel.
The substitutions gave the visitors an attacking impetus they had lacked for much of the match as they forced Brighton on to the back foot, though Gowling's header over the bar was the best chance they could muster.
In the 63rd minute Andy Barcham pounced on Tommy Elphick's misplaced pass and fed Jackson in the area, fortunately for the home side Elphick made up the ground superbly and dived in to make amends with a last ditch block.
Ten minutes later Brighton caused panic at the opposite end as Thornhill's cross was headed goalwards by Dickinson, Richards blocked before Royce made a stunning finger tip save to deny Andrew Crofts blast from the edge of the box.
Juat as Gillingham seemed destined to score, the Seagulls found the net from a well worked corner routine. Bennett exchanged passes with Thornhill before crossing for Elphick to plant a powerful header beyond Simon Royce.
The visitors continued to labour but their efforts produced no reward and fans will hope for a change of fortunes at MK Dons on Saturday.
Attendance: 5960 (372 Gillingham)
Gillingham: Simon Royce, Barry Fuller, Josh Gowling, Garry Richards (Jacob Erskine 88), Mark Bentley, John Nutter, Curtis Weston, Jack Payne (Stuart Lewis 51), Adam Miller (Dennis Oli 51), Andy Barcham, Simeon Jackson.
Subs not used: Alan Julian, Luke Rooney, Chris Palmer, Kevin Maher.
Brighton: Michel Kuipers, Gavin Hoyte, Tommy Elphick, Adam Virgo, Jim McNulty, Elliott Bennett, Gary Dicker, Andrew Crofts, Matt Thornhill, Nicky Forster (Liam Dickinson 46), Glenn Murray (Gary Hart 67).
Subs not used: Jake Wright, Dean Cox, James Tunnicliffe, Arron Davies, Greame Smith.