His stunning third-minute free-kick from almost 30 yards out flew into the top right-hand corner of the net and settled a scrappy and what for the Mariners was a ‘derby’ encounter and enhanced his reputation.
The lunch-time victory took Rovers to the summit before Plymouth and Carlisle won their games later in the afternoon.
Mandeville’s sixth goal from nine starts also coincided with a new role for the 19-year-old, who only returned from a loan spell at Whitby Town 12 months ago.
He moved back behind the front two strikers into the position vacated through James Coppinger’s three-match suspension caused, ironically, by sticking up for the youngster when his penalty had struck the post at Plymouth the previous week.
The No 10 role may eventually be Mandeville’s best position, believes manager Darren Ferguson, who is pleased not only that he took the Football League’s young player of the month award but also that his exploits have begun to attract the scouts.
“Mandeville is playing really well and the execution for the goal was really outstanding,” said the Rovers chief.
“What you have seen today is that he took responsibility; he wanted the ball all the time; he found pockets of space and was very confident on the ball though he sometimes overran it. The boy’s a good player and it’s amazing what confidence can do for someone.
“There’s a lot of clubs looking at Mandeville but when a 19-year-old goes on a run like he’s been having that is always the case in football. I am not worried about it because it is part and parcel of football and it is about time it happened at a club like this where the young players are getting noticed.
“The boy is happy playing football and when you get a 19-year-old, at no matter what level, starting to play well and scoring goals, news quickly goes round. I think we will hang on to him.”
Ferguson said he decided on switching Mandeville almost as soon as Coppinger saw red.
“I think he can play both roles, there is no question about it. I don’t want to say he replaced Copps because they play differently. Coppinger is also in very, very good form but one thing Liam gave us was a bit more size against a big, big team.
“The only thing I look at is the team. It doesn’t bother me who plays. They have just to make sure that they get to the standards that I expect.”
Level-headed Mandeville would not entertain the thought that one day he might replace club legend Coppinger.
Of his goal, which was reminiscent of the one scored by Orient’s Callum Kennedy in the previous home game when Mandeville netted twice from the penalty spot in a 3-1 win, he revealed: “That wasn’t what was planned.
“Rowey (Tommy Rowe) was meant to have a shot when I played him down the side but he said have a shot if it wasn’t on and from that moment I was always going to hit it!”
Mandeville went close again after the break with a curling free-kick down low to James McKeown’s left but the Grimsby goalkeeper went full length to push it away.
“Yeah I did enjoy playing in the Coppinger role but it was difficult as Grimsby made it very compact,” said the match-winner.
“I didn’t make the best start but I do enjoy that role. I used to see myself more as a No 10 but I have grown more into the striker’s role. They are large boots to fill, the Copp’s position, and there’s no chance of me taking it really.”
Of the rest of the campaign and his future, he continued: “Promotion is everything to the team. That is what we want and we are on course with two points per game. That will see us through.
“It’s going well for me at the moment and long may it continue. I wasn’t expecting any of this to happen so soon. I am loving every moment of it. I don’t think about any speculation. I definitely feel we can stay in the top three. It is just how react when we do lose games, which is inevitable, which will count.”
Mandeville was not the only player to switch. Matty Blair dropped from midfield and shone at right-back after Craig Alcock suffered a back problem which is unlikely to keep him out of the Boxing Day trip to Notts County.
Harry Middleton came in alongside Rowe in the centre, while Andy Williams returned up front to help Rovers match the physicality of the opposition.
There were some raw-boned challenges but Rovers showed they can cope and adapt when knocked out of their inter-passing stride.
They kept their first clean sheet in seven games though the Mariners still posed a threat, particularly through Tom Bolarinwa’s pace. Central defender Danny Collins headed wide from a free-kick, Blair made a fine intervention to clear a dangerous cross and Bolarinwa’s shot was blocked for a corner before a last-minute cross whistled across the area.
Doncaster Rovers: Marosi, Blair, Butler, Baudry, Mason; Houghton; Middleton (Wright 87), Rowe; Mandeville; Williams (Calder 72), Marquis. Unused substitutes: Jones, Garratt, Keegan, Beestin, Longbottom.
Grimsby Town: McKeown, Mills, Pearson (Jones 83), Collins, Andrew; Bolarinwa, Cornley, Summerfield, Berrett; Jackson (Tuton 77), Vernon. Unused substitutes: Davies, Gowling, Chambers, Disley, Henderson.
Referee: R Clark (Northumberland).