Cheltenham striker Steven Gillespie got the only goal of a game that promised more during a bright opening.
With 24 minutes played the former Bristol City striker raced onto a pass from Jerry Gill with the Gillingham defence appealing frantically for offside.
No flag was forthcoming and Gillespie rolled a shot beyond goalkeeper Simon Royce to make it 1-0.
Gillespie had earlier missed a similar chance and David Bird saw a header cleared off the line by former Cheltenham player Craig Armstrong as the Robins began brightly.
Gillingham had offered little as an attacking force in the first period but they started the second much better and Cheltenham goalkeeper Shane Higgs got down to save well from Delroy Facey.
However, things went even further wrong for them with 57 minutes played when defender Ian Cox, who was sent off in the corresponding fixture last season, hauled back Paul Connor a good 40 yards from goal and was sent off for denying a goal-scoring opportunity.
Former West Ham and Manchester City midfielder Steve Lomas followed him in the 75th minute for a second bookable offence but the most bizarre red card arrived 11 minutes from the end.
Gillespie, already booked for diving, turned his back as defender Nicky Southall placed a free-kick and began walking away. Southall struck the free-kick against his back and the referee produced a second yellow card then a red one.
Cheltenham missed two chances late in the game to make the game completely safe but overall it was a successful afternoon for John Ward's young side.
But Gillingham boss Ronnie Jepson was left seething at the match officials.