After a quiet opening Gillingham were the first of the two sides to settle, Curtis Weston testing Posh keeper Steve Collis with a speculative effort that flashed wide of the left hand upright. Three minutes later Andy Barcham went closer after finding space on the edge of the box, striking a rising drive inches over the cross bar.
On 17 minutes a weak back-pass by Geohaghon allowed Stefan Payne through on goal but he fired his shot straight at Collis. From the resulting throw-on Geohaghon mistimed his clearance presenting Chris Palmer with an opening to rifle the Gills in front from the edge of the box.
Within moments of the restart Gillingham bagged their second, Palmer loading the bullets with a far post corner that Andy Barcham climbed above the defence to head inside the back post.
On the half hour mark Stefan Payne did well to rob Geohaghon again wide on the right of goal, he centred for Dennis Oli but Collis was able to gather his low finish at the second attempt. Payne himself went close four minutes later, with a drilled shot on the turn from inside the area, this time Collis made an impressive stop with his right leg.
Three minutes before the break the lively Payne drew another save from the Posh custodian with a snap shot from the edge of the box but the Gills were unable to extend their first time lead.
HT 2-0
After nine changes, at the start of second half, Gillingham surrendered the early advantage to Peterborough, trialist keeper Lance Cronin twice denying good chances for the visitors.
The home side responded on 51 minutes with Danny Jackman crossing to the far post but Serge Makofo could not find the finish that Jackman's delivery deserved.
Josh Simpson had a low effort well blocked by Cronin before Andy White netted the Gills third on 58 minutes. Luke Rooney's deep ball sent the young forward clear and White slotted coolly into the roof of the net from just inside the box.
Posh pulled one back on 64 minutes, Ben Wright turning Mark Bentley before rolling a neat finish wide of Lance Cronin and into the bottom corner. But their joy was short-lived as Luke Rooney added Gillingham's fourth four minutes later. Andy White crossed from the left, Stanley Aborah dummied and Rooney arrived to crash home from the penalty spot.
Serge Makofo was unlucky to see his effort come back off the woodwork on 75 minutes, after the trialist striker had showed good strength to hold off his marker, while Luke Rooney sliced wide after a great build-up involving White and Spiller.
Attendance: 1,064
Gillingham: Alan Julian (Lance Cronin 46), Barry Fuller (Mark Bentley 46), John Nutter (Danny Jackman 46), Jack Payne (Kevin Maher 46), Josh Gowling (Connor Essam 78), Tony Sinclair, Curtis Weston (Stanley Aborah 46), Chris Palmer (Danny Spiller 46), Stefan Payne (Luke Rooney 46), Dennis Oli (Serge Makofo 46), Andy Barcham (Andy White 46).
Peterborough United: Steve Collis, Josh Simpson, Scott Griffiths, Ramone McCrae, Exodus Geohaghon, Carl Piergianni, Danny Mills (Matt Breeze 64), Jay Davies (Lewis Bishop 73, Kgosietsile Ntlhe 78)), Rene Howe, Dominic Green (Joe Newell 84), Ben Wright.