Veteran striker Barry Hayles has not trained all week having been called up for a stint of jury service but the former Fulham and Leicester City hit man emerged from the substitutes' bench to turn this game on it's head in the second half.
Grimsby had dominated the first 45 minutes and looked a useful side in the process but things changed from the moment Hayles entered the pitch in the 54th minute.
He set up the equaliser for Lee Ridley - his first goal for the club - then pounced on a cross from David Hutton to grab the winner.
However, it was not all about Hayles during a very positive second half showing from the Robins. Elvis Hammond, Michael Pook and Hutton all put in impressive displays as Cheltenham Town got off the mark in their first game of the season.
TEAM NEWS: Three players were named for their competitive club debuts. Midfielders Michael Pook and Oliver Bozanic were joined in the starting line-up by striker Justin Richards.
Defender Michael Townsend did not make the starting line-up due to slight a knee injury, while striker Barry Hayles was named among the substitutes.
The other new faces in the squad were defender Jordan Tabor, goalkeeping player-coach Barry Richardson and returning striker Julian Alsop, who were all named among the seven substitutes now allowed by Coca-Cola League rules.
1st minute: There was an all-action start to the contest with both sides having free-kicks in promising positions within the opening minute. David Hutton's effort for Cheltenham was cleared by the visiting defence while Grimsby's Peter Sweeney hit his shot into the defensive wall.
3: Grimsby midfielder Nick Hegarty got onto the end of a right-wing cross from striker Adam Proudlock but his effort was well wide.
4: A great chance for Grimsby when veteran striker Barry Conlon launched himself onto a cross from Hegarty but Cheltenham goalkeeper Scott Brown made himself big and blocked the header. Lee Ridley completed the clearance.
6: Hutton received a pass from Richards on the edge of the penalty area but his shot lacked the power to beat diving Grimsby goalkeeper Nick Colgan.
11: Cheltenham were handed another free-kick right on the edge of the penalty area when Ryan Bennett committed a foul on Richards. David Bird tried a right-footed curling shot but chopped it over the crossbar.
14: It was fast and furious stuff in the opening 15 minutes and Grimsby had the next chance when right-sided midfielder Chris Jones laid the ball back to Sweeney on the right-hand corner of the Cheltenham penalty area. Sweeney hit a low, skidding shot that was creeping inside the near post until Brown got a hand to it and turned it aside for a corner.
20: Cheltenham created a decent chance on the counter-attack when Grimsby lost possession on the edge of the Robins' area. Hutton chased onto a long ball and squared it for Richards, whose low shot from 18 yards brushed the outside of the goalkeeper's right-hand post.
24: A dangerous in-swinging free-kick from Hutton caused all sorts of problems in the Grimsby defence. Elvis Hammond managed to turn sharply in the box and his shot was kicked off the line by Ryan Bennett. However, the assistant referee had already flagged Hammond offside.
29: A long clearance by Brown was touched on by Richards to Oliver Bozanic. The young Australian knocked it back into the path of Andy Gallinagh but his shot cleared the crossbar. Bozanic tried his luck from a similar position shortly afterwards but he also failed to keep his shot down.
35 GOAL: A very well-worked goal by Grimsby Town that resulted from a move of several passes. The Mariners had already had possession for a few seconds when Sweeney and Proudlock combined well in the centre of the pitch to work some space. Sweeney sent Proudlock away down the inside right channel and he got right to the byline before dragging a cross back across the goalmouth. Drissa Diallo challenged with Conlon at the far post but was not able to get the ball clear and it bounced off Conlon and over the goal line.
36 YELLOW CARD: Grimsby's Barry Conlon for over celebrating the goal
38: Another good chance for Grimsby when midfielder Danny Boshell bent a free-kick edge of box just wide of the far post.
45: Elvis Hammond tried a right foot shot from the edge of the box but Colgan was down to save comfortably.
HALF-TIME: Cheltenham Town 0, Grimsby Town 1
47: Cheltenham made a promising start to the second half and a move of several passes ened with a left-foot shot from Bozanic that was deflected wide for a corner.
48: The Robins kept the pressure on from the flag kick and when Hutton found Bozanic inside the box the Australian smashed another deflected shot, this time against the angle of post and bar.
49: A long, raking pass from Bennett found Hegarty wide on the left. He cut inside and although his initial cross was half-cleared by Drissa Diallo, Hegarty followed up with a low drive that Brown got down to save at full length.
53 SUBSTITUTION: Barry Hayles entered the field in place of Oliver Bozanic. Hayles went up front alongside Hammond with Richards switched to the right-hand side.
54 GOAL: Hayles had an immediate impact on the game, beating two men deep inside his own half then spreading a pass across field to Lee Ridley on the left. Ridley cut inside onto his right foot and thumped a shot at goal that may have taken a deflection on its way past a static Colgan for his first goal in a Cheltenham shirt.
59: Hayles cleverly left the ball on the edge of the box for Hammond, who flipped it back across for the substitute but his shot went wide. The introduction of Hayles had certainly breathed new life into the Cheltenham performance.
61: Ridley had clearly enjoyed his goal and got forward again just after the hour mark for another right-foot shot that went just wide of the far post.
64 SUBSTITUTION: French striker and former Cheltenham Town trialist Jean-Louis Akpa Akpro replaced Chris Jones wide on the right.
66 GOAL: A patient build-up by the Robins ended with a slightly overhit through ball from Pook that Hutton took superbly in his stride. Hutton squared it across the face of goal and Barry Hayles was on hand for a far post tap-in.
68: Hutton broke free onto a long ball from Pook with the Grimsby defence back-tracking but he dragged his shot wide of goal.
69 YELLOW CARD: Bennett booked for a foul on Hammond.
72 YELLOW CARD: Hayles cautioned for a foul on Sweeney 25 yards out in a central position. Sweeney took the free-kick himself but fired it into the defensive wall.
78: Cheltenham continued to look the more likely team to score and when Pook sent Hammond free with another good through ball, the former Leicester City man turned onto it sharply but hooked his shot across the face of goal.
81 SUBSTITUTION: Josh Fuller replaced Hegarty for Grimsby Town.
84: Hammond produced a wonderful turn on the edge of the box onto a pass from Bird but was unable to replicate that quality with his shot at goal.
88: Another chance for Hammond, this time from another pass from Pook. Hammond strolled past left-back Joe Widdowson and into the area but blasted his shot into the side netting.
90 SUBSTITUTION: Julian Alsop back at Cheltenham after six years went on for Hammond.
90+1: Two late scares for the Robins when first Robbie Stockdale sent a deflected shot wide then, from the resulting corner, Conlon found himself in space 12 yards out but screwed his shot wide.
FULL TIME: Cheltenham Town 2, Grimsby Town 1
CHELTENHAM TOWN (4-4-2): Brown; Bird, Diallo, Duff, Ridley; Hutton, Pook, Gallinagh, Bozanic (Hayles 53); Hammond (Alsop 90), Richards. Other subs: Richardson (Gk), Townsend, Haynes, Watkins, Tabor
GRIMSBY TOWN (4-4-2): Colgan; Stockdale, Bennett, Atkinson, Widdowson; Jones (Akpa Akpro 64), Sweeney, Boshell, Hegarty (Fuller 81); Proudlock, Conlon. Other subs: Overton (Gk), Clarke, Linwood, Leary, North
ATTENDANCE: 3,654 (752 from Grimsby)