Prior to kick-off at Moss Lane, the Blues needed just a point to book a place in the division’s top five and Leon Mettam’s terrific hat-trick earned Steve Housham’s men all three.
The former Lincoln City youth striker struck twice in the first period, including a superb 20-yard free-kick, and scored what proved to be the winning goal 18 minutes from time as Trinity completed the double over the Robins.
The victory guaranteed the Blues a fourth-placed finish and sets up a play-off semi-final tie with FC Halifax, who finished ahead of them in third.
“All this hard work my players have done has paid off and now we’re in the play offs – let’s go and win it,” said a delighted Housham.
“It’s been a good season and you can’t take that away from the players but it’s not a great season until there are medals on the table and that’s what we’ll be trying to do now.”
“We are three games away, one draw and two wins and we could be in the Conference Premier.”
Trinity face the Shaymen in the first of those games at the Northolme on Wednesday evening and former Brigg Town boss Housham is expecting another difficult game against the West Yorkshire outfit.
“It’s going to be another tough one, but a great game for the players to play in where there could be a crowd of three thousand plus at both games,” added Housham.
“We owe a lot to our fans this season because it’s been a troublesome time for them over the past few years but now they have got something to smile about.”
“We’ll only get a big smile from everyone when we reach the final of the play-offs and that is what we want to do.”
And the Blues chief was full of praise for hat-trick hero Mettam at Altrincham and says his performances have given him a real selection headache for the play-offs with Ryan Kendall also on the mend from injury.
He told the Standard: “He’s (Mettam) had to bide his time this season but when he has come in he has shown what he can do and I am delighted for him.”
“But everyone has dug deep and we have all stuck together and that was shown on Monday when the whole squad came in to train.”
“It is not in their contracts to come in and the togetherness is one of the best I have seen anywhere when I was a player and now as manager.”
“When you have that togetherness that is half the battle already and we have got a great team spirit.”
And despite a few early scares against eighth-placed Altrincham, Mettam’s superb free-kick flew into the top corner via the underside of the crossbar to put Trinity ahead on 13 minutes.
Alty’s Nicky Clee restored parity just after the half hour mark with a powerful shot which gave Trinity stopper Jason White no chance and the hosts edged ahead three minutes before half-time after Duncan Watmore’s exquisite dink over White.
But in first-half stoppage time Mettam added his second of the afternoon glancing home Ryan Williams’s to beat home custodian Stuart Coburn.
After the break, both teams pressed forward in numbers but it was left to that man Mettam again to complete his hat-trick and claim the match ball on 72 minutes.
Despite the Alty protests, Mettam beat the offside trap before rounding Coburn and slotting into an empty net to make it 3-2 to Trinity.
The Robins struck the crossbar in the dying moments and Andrew Boyce had to be on hand to hack away a goal-mouth melee as the home side searched for another equaliser.
Despite the two minutes of stoppage time an Altrincham goal failed to materialise and Trinity were greeted off the field by the travelling support behind the goal.
Man of the moment Mettam refused to take all the plaudits after his three-goal haul and said it was important for the team to bounce back after the 2-2 draw at home to Worcester the previous week.
Mettam said: “It is nice to get out there and get a win and we needed it after last week and to get three goals is always nice as well.”
“We have still got some massive games to come, massive for the club and massive for everyone involved from the gaffer down to the kit man.”
“All the hard work that everyone has put in is hopefully going to pay off if we get promoted to the Conference Premier.”
Altrincham FC: Coburn; Densmore, Smart, Phelan, Flynn, Broomes, Lawrie, Richman, Watmore, Reeves, Clee. Subs (not used): Lynch; Miles, Twiss, Grimshaw, Reid.
Gainsborough Trinity: White; Roma, Sandwith, Boyce, Waterfall, D’Laryea, Clarke, R. Williams (J. Williams 65), Yates, Stamp (Connor 46), Mettam (McMahon 90). Subs (not used): Watts, Thewlis.
Goals: Clee 23, Watmore 43; Mettam 13, 45, 72.
Referee: Mr S. Oldham.
Assistants: Mr D. McNamara, Ms N. Walker.