Swindon scored just after four minutes when a collision between Bristol Rovers goalkeeper Steve Phillips and defender Byron Anthony left a loose ball, which Simon Cox pounced on to calmly place the ball into an empty net from 20 yards.
Anthony received extensive treatment before being stretchered off and replaced by Darryl Duffy. Phillips, although appearing to be very shaken, was able to continue.
Billy Paynter might have made it 2-0 almost immediately, but Phillips did very well to block the home striker's effort.
It was another rather fortunate goal which levelled matters for the visitors when Kevin Amankwaah's clearance rebounded from Duffy's foot and the ball skidded past goalkeeper Smith who had no chance of saving.
Chris Lines might easily have given Rovers the lead before half-time when his shot from 25 yards was destined for the top corner, but Smith reacted brilliantly to tip the ball away for a corner.
Rovers had looked the much more likely winner in the first half, but Swindon played with a lot of spirit but they lacked at times any quality.
Rovers top scorer Rickie Lambert saw his shot blocked by Jerel Ifil in the early stages of the second half as Rovers looked far the better side and, at this stage, Swindon were showing why they were in danger of being relegated.
But the home side picked up their game and first Paynter and then Cox saw headers go narrowly wide, but it was top scorer Cox who scored his 30th goal of the season in the 81st minute to pinch the game for Swindon.
Good work by substitute Jon-Paul McGovern and Amankwaah led to a fairly indifferent cross which Rovers failed to clear and Cox turned to hit the ball past Phillips to send the home fans into raptures.
A good game, played in a good spirit, no bookings and these two teams will meet again next season.