Extra-time goals from George Darling, Buster Harradine and Connor Wood completed a thoroughly deserved 4-1 victory for Steve Fallon’s men as Soham booked their place in the second qualifying round of the FA Trophy.
The hosts looked to be heading to a 1-0 win in normal time thanks to Luke Stanley’s 20th minute opener but with just seconds remaining, Grantham substitute Adie Hawes fired home an equaliser.
The dismissal of Gingerbreads substitute Gary King immediately afterwards helped Soham’s cause and they duly took advantage in the extra period.
The climax was quite a contrast to the relatively cagey opening to the match.
Buster Harradine made a strong run that nearly led to the game’s first goal in the opening quarter of an hour but his final pass could not find a Soham team-mate.
Jamie McGhee fired a free-kick over for the visitors before the deadlock was finally broken in the 20th minute.
Stanley picked up the ball on the right deep into Grantham territory and ran across the face of the penalty area before letting fly with a low left-foot shot that rolled into the bottom corner.
Grantham created little in the final third and it was the hosts who came closest to scoring in the final stages of the first half with James McCabe having a header saved and Stanley only just failing to connect with Harradine’s dangerous cross.
The second half saw Soham continue to control the game but they were especially dangerous on the counter-attack.
Stanley and Harradine both got behind the Grantham defence but were unable to get a shot in on goal.
Substitutes Ben Sawyer and George Darling also impressed when they came on and in the 79th minute the former had a great chance to extend the lead when he raced through on goal and lobbed Grantham keeper Jake Turner, only to see his effort drift wide.
As the game became more stretched, Grantham’s best chance of an equaliser came two minutes later when Michael Towey hit a well struck shot from 25 yards that Soham’s Leigh Follen did well to hold on to.
Deon Meikle had a header saved with three minutes remaining as Grantham chased an equaliser and it eventually arrived in the 89th minute when substitute Adie Hawes fired home at the near post.
Just moments later Grantham were reduced to 10 men when King was shown a second yellow card, with the match then going into extra time.
It took just three minutes from the restart for Soham to go back in front, Darling drilling the ball home with a neat finish just seconds after Grantham’s McGhee had seen a shot saved by Follen.
The hosts dominated the final 30 minutes and although Grantham went close with a shot from Greg Smith that Follen did well to keep out, a superb goal from Harradine made it 3-1 in the 109th minute.
Wood applied the finishing touch with Soham’s fourth goal four minutes from time.