Spalding stormed to a superb bonus-point win thanks to five top-class tries.
They were hanging on in the first half with Grimsby taking control.
But Justin Cole, standing in for coach, George Reid had his ‘providers’ coming off the bench who made a difference.
Grimsby got two early tries until Spalding’s defensive shape sharpened up as they pressed to close space, led by centres George Brown and Adam McHugh.
Grimsby lost the ball deep in Spalding’s half and it was then spread quickly along the backs to Gav Sharman who showed his pace to outstrip everybody to open the away team’s account. But in doing so, he pulled his hamstring with Fin Peters replacing him.
Spalding’s scrum was again looking very secure, led by props Pete Waudby and Pete Smith, as hooker John Barrett burst forward to gain 30 metres.
The momentum continued and was finished off as Ash Piccaver broke through a couple of tackles to go over in the left corner – pulling them level on points.
Grimsby immediately responded and Spalding’s press defence was caught offside twice.
Harry Cole received a yellow card for the second offence with just five minutes of the first half remaining.
The home team took full advantage of the extra man – helping themselves to two tries and a half-time lead of 22-10.
Jason Steels came on for Cole and immediately made an impact.
From a scrum Steels picked up and gained a 20 metres. Peters continued the move down the left, cut back inside and McHugh was on hand to crash over the try line.
Just a couple of minutes later, Spalding came right back into the game.
Scrum-half Ben Shields, who had an excellent game, popped the ball out to fly-half Dan Adams who offloaded to George Brown to run between the posts. With Ashton Capes converting, the scores were level.
Back came Grimsby through their forwards to go five points up.
With the ball flowing along the backs in open play, pulling Grimsby apart, McHugh got his second try of the afternoon.
Steels again made a break across the field, Piccaver continued the move and Harry Brown scored between the posts, converted by Capes.
The home team were in disarray, unable to cope with Spalding’s running game.
Peters lit up the dull afternoon with a mazy run down the left wing – beating four or five defenders and tackled just a few metres short – but George Douglas was in support to cross the line with Capes again converting.
With a 14-point lead and eight minutes remaining, all Spalding needed to do was close the match out.
Grimsby’s hooker was yellow-carded, which in effect sealed an excellent win for Spalding from the best away performance of the season.
Spalding: Waudby, Barrett, Smith, Cole, Piccaver, W Shields, Cooke, H Brown, B Shields, Adams, Sharman, G Brown, McHugh, Capes, Douglas. Subs: Steels, Peters.