With two minutes gone, there was an early attack for the Iron, started by Cameron Wilson in midfield before play spread to the left with Jordan Hallam. The ball then ended up on the right, with Alex Perry’s deflected cross looping up for the ‘keeper to gather.
Finley Shrimpton got the game’s first yellow card as a ball in behind saw the Grantham forward hit the deck. The hosts were rewarded a free-kick 25 yards from goal, which was dealt with by the Iron wall.
With nine minutes played, Perry won the ball and played Wilson in down the left flank, and he sent in a searching cross which nobody could get on the end of.
At the other end, three minutes later, Grantham sent a free-kick in from deep but nobody could connect and the ball whistled past the post.
With 15 minutes played, Harry Jessop saw a long range effort blocked as he and Kenan Dünnwald-Turan tried to work an opening.
Two minutes later, Dünnwald-Turan came close to opening the scoring, as he received the ball down the right flank from Dan Gallimore and checked inside before firing an effort onto the top of the netting.
Just moments after, Myles Hippolyte drove through the centre and played Hallam through, but his dinked effort went over the bar.
Then, the Iron played the ball neatly around the Grantham penalty area, which resulted in play finding O’Malley on the right side. His in-swinging cross searched for Jai Rowe, with his diving header going into the side-netting.
Hippolyte took a free-kick from the edge of the box in the 28th minute, curling his effort over the wall, but also over the crossbar.
Then, two minutes later, Wilson charged down an attempted clearance from the Grantham right-back and then looked to work space for a cross. He cut back for Jessop before Hallam almost got the loose ball just inside the area.
In the 36th minute, at the other end, Shrimpton calmly moved the ball away from the goal mouth following a loose ball in the penalty area.
Soon after that, O’Malley’s cross into the box from the left left the home shotstopper scrambling, but the ball flew across the box and out of play for a throw-in.
With 39 minutes gone, the host’s number nine turned onto his right foot from range and looked to loop a long range effort towards goal, which cleared the crossbar.
Two minutes after, they came close again as Watson made a brilliant one-handed save from the same Grantham player, who tried his luck from just inside the area, as he tipped over for a corner.
Just before the half-time break, Wilson linked up with Hallam on the left flank and the former's cross caused confusion in the Grantham area before being cleared.
After 48 minutes, Dünnwald-Turan broke clear of his marker inside the area and brought the ball down just wide of the six-yard box. He lifted the ball over the ‘keeper but also over the bar.
Three minutes later, Hallam and Wilson combined down the left before Hallam teased the defender to challenge, with the ball going out for a throw. Both then combined soon after as Hallam saw a 20-yard effort blocked.
After 56 minutes, the hosts broke away with the ball, with a left-winged cross met with a header, which Watson was more than equal to as he got down to his left to grasp.
Three minutes later, Wilson was almost in on goal, slipped in by Hallam, following a good move, but the home goalkeeper was sharp off his line to sprawl on top of the ball.
With 65 minutes gone, Grantham cleared off the line to deny Hallam. The Iron frontman was slipped in, he rounded the goalkeeper and saw his shot blocked before his follow-up cross was recovered by the goalkeeper.
Then, Jordan Hallam was replaced by Under-18s attacker Harrison Poulter.
Rowe dinked a good ball into Perry inside the area in the 69th minute. He initially did well as he tried to feed the ball between two players, managing to hold onto possession before the hosts crowded him out and hacked the ball clear.
In the 71st minute, Poulter chased the ball all the way back to the Gingerbreads’ goalkeeper and almost charged down his clearance, with the ball only taking a deflection and ending up in Grantham possession.
There were a further two Iron changes as Under-18s players Oliver Lobley and Ben Franklin came on for Gallimore and Hippolyte.
Shortly after, Poulter held up play inside the area and saw two shots blocked, with one minor handball shout waved away by the referee. Perry then tried his luck from range, but the ball sailed wide.
With 82 minutes gone, Poulter turned his man right on the edge of the box and was hauled down. A free-kick was given, but no card, despite the defender being the last line of defence.
And from the free-kick came the decisive goal as O’Malley took it, bending the ball over the wall and into the roof of the net.
Two minutes after, at the other end, the hosts wanted a penalty as a Grantham man stumbled in the box, but the referee dismissed the claims.
With 87 minutes played, the Iron broke in numbers following a Grantham attack. Jessop opened out onto his left foot from 25-yards and stung the hands of the goalkeeper, who gathered at the second attempt.
On 90 minutes, Shrimpton went on a marauding run and sent a long range low effort towards goal which was saved as three added minutes are indicated. During those, Jessop received a late yellow card from the referee but United held on for the win.
The Iron's League Two season starts on Saturday when they host Swindon Town (3pm kick-off).
IRON: Watson, Gallimore (Franklin, 78), O'Malley, Perry, Rowe, Shrimpton, Wilson, Hippolyte (Lobley, 78), Jessop, Hallam (Poulter, 66), Dünnwald-Turan.
IRON SUB NOT USED: