The Iron made three changes ahead of the game, with Jake Leake, Dion Sembie-Ferris and Tom Pugh coming in for Cameron Wilson, Finley Shrimpton and Colin Daniel.
The first chance of the game came in the second minute when Danny Elliott received the ball midway through the Dorking half and turned before unleashing an effort wide of the home goalkeeper's right-hand post.
Soon after, the hosts won a couple of free-kicks near the Iron's 18-yard box, and sent the ball but United managed to get the ball clear.
They drew a first save from Owen Foster in the 20th minute when James McShane's driven effort from the edge of the area came about following a set-piece from the left that was only partly cleared.
Seb Bowerman was next to test Foster with a low drive from the right side of the box, which was palmed away.
In the 24th minute, there was a superb double save from Foster as he got down low to his right to deny one shot before he thwarted the rebound at the striker’s feet from a couple of yards out. A further block came in from Dean Rance before the Iron got the ball away.
On the break, instigated by Reagan Ogle driving forward, Elliott eventually received the ball on the left before flashing a cross, across goal but unmet.
With 29 minutes played, the hosts took the lead as a low ball into the box was converted into the right corner of the net by Ryan Seager.
Not long after, a long throw from Jake Leake was headed on by Andrew Boyce before being cleared. Boyce then crossed for Elliott who saw his header gathered by Dan Lincoln.
On 40 minutes, McShane cut onto his left foot on the edge of the box and sent an effort just wide of Foster’s right-hand post.
Then, Foster was tested again as the hosts played the ball towards the edge of the box, with the Iron shotstopper making a comfortable stop.
Early in the second half, Taylor took a free-kick for the hosts, curling a free-kick into the area and out for a goal kick.
Soon after, Bowerman sent a first time effort just over the bar as the ball was rolled to him on the edge of the box from the right.
On 53 minutes, Elliott sent an effort over the bar for the Iron following a knockdown to the edge of the box as the Iron worked play down the left.
Then, Will Smith brought the ball forward 50 yards following a throw from Leake and was allowed to get within 25 yards of goal. His low strike was turned away for a throw before the Iron won a free-kick on the right.
Pugh peeled away at the back post from the free-kick, with his header gathered by Dan Lincoln in the Dorking goal.
As United grew more into the game, there was a smart turn by Leake as the ball was threaded through to him. He ran into the box before drawing a save from Lincoln.
But they were soon punished again at the other end as, on 60 minutes, Seager struck his second goal of the game, from just inside the area.
There was a double Scunthorpe change straight after as Josh Robertson and Shrimpton came on for Pugh and Rance.
The hosts threatened again soon after, when a ball was fizzed across from the right and Seager connected with his head but turned the ball wide.
On 67 minutes, Ottaway was denied a third for Dorking by Foster as he beat his effort around the post for a corner. Craig then headed wide the resultant corner.
A minute later, Carver headed wide for the Iron following play from Shrimpton and Sembie-Ferris which saw the substitute dink in a cross for Marcus Carver.
Foster saved again as Briggs got in behind, with Foster pushing the effort around the post for the corner.
There was a good interchange on halfway which sent Sembie-Ferris on his way. He cut across the box to Sean Shields, with the fingertips of Lincoln denying the Iron winger from scoring.
Scunthorpe made their final change on 75 minutes when Jacob Butterfield came on for Sembie-Ferris.
The Iron pulled one back in the 82nd minute. Robertson and Butterfield pressed to win the ball back and force the ball to Elliott, who controlled turned and found the bottom corner of the net.
On 87 minutes, Robertson was slipped in down the right and saw his cross turned behind for a corner. Smith connected to Butterfield’s corner, but he couldn't angle his header on target.
In the second minute out of four in stoppage time, Ogle was fouled but the referee didn't award a free-kick. Shields stole in and won the ball. He was fouled but the referee played advantage for that infringement before Elliott saw his shot saved.
DORKING: Lincoln, Taylor, Muitt, Seagar (El-Abd, 88), McShane, Gallagher, Fuller, Ottaway, Kuhl, Craig, Bowerman (Briggs, 62).
DORKING SUBS: Philpot, Harris, Ottaway.
IRON: Foster, Ogle, Elliott, Boyce, Carver, Leake, Sembie-Ferris (Butterfield, 75), Smith, Pugh (Robertson, 63), Rance (Shrimpton, 63), Shields.
IRON SUBS: Daniel, Bennett.
ATTENDANCE: 3,006 (185 away).