A poor back pass in the fourth minute by Izzy Iriekpen almost led to the visitors taking the lead. Andy Keogh raced in to meet the ball before it reached Swans keeper Willy Gueret but his shot towards an open goal was deflected behind for an unproductive corner.
Keogh was lively down the right flank in the opening minutes as the Iron pushed the Swans back in defence.
Andy Butler was given a severe warning by referee Paul Armstrong after pulling back Adebayo Akinfenwa.
As he had been booked as early as the eighth minute he was now treading dangerous ground.
With the half drawing to a close the Swans were gaining the upper hand with the Alan Tate and Leon Britton partnership working well down the right.
Although neither side were playing badly the game needed a spark to set it alight.
It came in the 53rd minute when Britton was set free down the right flank. He cleverly pulled a low cross into the path of Robinson who side-footed into the net to put the Swans ahead.
Lee Trundle and Britton then opened up the visiting defence but Akinfenwa's snap-shot whistled past the post.
Iron boss Brian Laws brought on Wayne Corden and Cleveland Taylor in the 67th minute in an effort to rescue something from a game that was now slipping away from them.
Butler had the ball in the home net following a Peter Beagrie corner but it was disallowed for a foul on Gueret.
Goalscorer Robinson was replaced by Forbes in the 82nd minute and four minutes later the home side had the points in the bag.
As the visitors went on the attack, the Swans broke clear and an inch-perfect pass from Trundle put Forbes away and he calmly slotted home to seal a hard earned victory.