In the first half he denied Shaun Miller and near the end Paul Mullin after two controversial decisions by referee Mark Heywood, the second which saw boss Adam Murray sent from the bench after an angry clash with the official.
Good football was difficult on a pitch hampered by rain and strong, swirling winds, but both sides somehow managed to conjure up a good spectacle.
Stags had gone behind in the opening minute to a Kevin Ellison goal, but Matty Blair levelled via a deflection on 15 minutes and Krystian Pearce put them in front nine minutes later.
Shearer made his first penalty save a minute later before his second near the end as the home crowd screamed at the referee.
But Stags clung on for a rare home win and were cheered off the pitch.
Mansfield made just one change with Craig Westcarr in for the suspended Matt Green.
Green had to sit the game out after two yellow card offences at Crawley Town last weekend.
Stags were looking for a third successive win for only the second time this season and a 12-day double over the Shrimpers after winning 2-1 away there on 26th January.
New signing, Swansea full back Daniel Alfei had to be content with a place on the bench.
The referee had two morning inspections of the wet pitch before deciding it was playable.
However, Stags could not have made a worse start on the sodden surface.
Collins tried to get the ball away with a diving header just outside the home box, but it struck Pearce and fell nicely into the path of Ellison, who drilled a superb finish inside the right post.
It was the sixth time in seven games the Stags had conceded at home.
McGuire headed away two Morecambe corners before Stags forced their first on 11 minutes.
McGuire met it with a soft shot that was cleared, only for the clearance to hit Pearce and fly back at Roche.
But Mansfield were level on 15 minutes.
Blair tried his luck from 25 yards and the ball clipped the head of Edwards en route which took it up and over a helpless Roche.
Soon after Westcarr battled his way to the left by-line and crossed low, Roche just beating Baxendale to the ball.
On 22 minutes Pearce headed the ball away as far as Ellison on the edge of the box, who stabbed a shot on target only to see Shearer well placed.
Three minutes later the Stags were ahead.
Benning sent in their second corner from the right and Pearce powered home an unstoppable header from six yards.
A minute later Stags had a let-off as Devitt picked out Ellison at the far post, where he put the ball into the net only to see an offside flag already raised.
They had an even bigger let-off on 25 minutes as Shearer made a superb save from a Miller penalty.
The award looked harsh as Goodall fed Fleming in the box and he went down easily as he turned Tafazolli. But the referee was on the spot, gave the kick and booked the Stags defender.
Miller tried to place it to the right of Shearer, but he guessed right and turned the ball away to huge cheers.
A minute from the break Clements let fly from 30 yards to force a great save from Roche, diving to his left.
Stags made the early running and stoked up the pressure after the break.
But the first save was by Shearer as he clung onto an on-target Ellison free kick from 30 yards on 53 minutes.
On 58 minutes Benning stepped up to take a free kick from wide on the right and tried to catch Roche napping with a curler to his near post, the keeper down to push away.
A minute later Stags made the first change with Thomas on for Westcarr, leaving Beardsley on his own up front.
On 65 minutes a poor Dugdale clearance went straight to Baxendale, whose curling finish wasn’t far wide of the far post.
Then Devitt pulled a 20 yard shot wide from a Pearce clearance.
Morecambe made a double change on 72 minutes with Molyneux and Mullin joining the action.
Beardsley was too high with a shot on 72 minutes and then made way for Lambe.
At the other end a Devitt ball into the box went through everyone and Shearer was forced into a parry.
Sensationally, Morecambe won a second penalty of the afternoon on 84 minutes as Devitt hit the ball at Thomas right in front of him and again it looked harsh to give handball.
This time Mullin took it but Shearer was again the hero as he saved with his trailing leg.
The Stags bench was furious with the decision and after the referee went over, Murray was ordered to the dressing room.
Fleming was booked for a foul on 90 minutes.
Five minutes were added in which Ellison put a close range header over to jeers from the stands.
STAGS: Shearer, Collins (C), Pearce, Tafazolli, Benning, McGuire, Clements, Baxendale, Blair, Westcarr (Thomas 59), Beardsley (Lambe 78). Subs not used: Jensen, Chapman, Yussuf, Kavanagh, Alfei.
MORECAMBE: Roche, Dugdale, Edwards, Devitt, Barkhuizen (Molyneux 72), Ellison, Goodall (Wildig 82), Miller (Mullin 72), Fleming, Parrish, Conlan. Subs not used: O’Hara, Kenyon, Bailey, Doyle.
REFEREE: Mark Heywood of West Yorkshire.
ATTENDANCE: 3,090 (98 away).
CHAD STAGS MAN OF THE MATCH: Scott Shearer.
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