With the Imps slow off the mark Mansfield took the lead in the 21st minute when Matt Green got the better of Andrew Boyce before rounding Paul Farman and slotting home. City rallied though and deservedly levelled shortly before the break when Alan Power curled home a superb free-kick past Shane Redmond.
Jamie Taylor fired the Imps in front a couple of minutes after the restart only for Louis Briscoe to volley home superbly to make it 2-2. Again, City's heads didn't drop and in the 65th minute Power bagged his second when he followed up after Redmond had palmed away a Taylor shot.
City continued to dominate and came close to adding a fourth when Tom Miller volleyed against the bar but three minutes into added time, Stags' substitute Matt Rhead powered home a header to take the tie to a replay.
There was still time for City sub Vadaine Oliver to have a header hacked off the line from the last attack of the game but Rhead's dramatic leveller means the two teams will have to do it all again for a place in the Third Round.
City reverted back to the side that defeated League Walsall in the first round for this eagerly-anticipated FA Cup with Budweiser Second Round tie against Mansfield Town at The 12th Imp Sincil Bank Stadium.
In fact, if you take out last week's FA Carlsberg Trophy game at Tamworth, this will be the sixth successive match in which manager David Holdsworth has had the luxury of naming an unchanged starting line-up.
With bright sunshine greeting the two teams as they emerged from the tunnel, Mansfield kicked off attacking the Bridge McFarland Stand, but only after those present in the ground paid tribute to the late Bert Linnecor with a rousing minute's applause.
The Stags were the first to press with Paul Farman forced to claim a long Exodus Geohaghon throw-in after Matt Green was denied a shot on goal after the striker appeared to lead with an elbow on Andrew Boyce, who was left rubbing his head as a result.
City's response saw them win a throw-in of their own following good hold-up play by Jamie Taylor but after Geohaghon headed clear, Jake Sheridan was penalised for a trip on Lindon Meikle. This free-kick led to a 10th minute Mansfield corner which was well claimed by Farman.
A cagey opening continued with neither goalkeeper really tested in the first quarter of an hour but things livened up in the 18th minute when John Thompson went in high on Adam Smith with the right-back luck to escape with a yellow card to his name.
Shortly afterwards Green flicked a cross from ex-Imp Lee Beevers a foot wide of the target but the striker was quick to press forward again a minute later and after he latched on to a ball over the top, appeared to push Boyce before advancing forward. He duly rounded Farman and slotted into an empty net.
The Imps looked for a quick response and when John Dempster crudely scythed Sheridan down whilst the City man was in full flight, the Town man somehow escaped punishment other than the conceding of a free-kick as the decisions continued to go against the men in red and white.
Some hesitant City defending then gave Green another sight of goal but this time, after he rounded Farmann for a second time, he screwed his effort wide of the target, although in his defence he was wide and at a difficult angle.
The ball just wasn't running for the Imps with Boyce unable to create space after a Gray throw fell to him just inside the area; the throw coming into the box after Town 'keeper appeared to stamp on Jamie Taylor's foot inside the six-yard box.
Taylor then tested Redmond with a 25-yard free-kick as the half entered its final five minutes before Peter Gilbert headed a Power cross goalwards only for Redmond to gather again.
City kept up the pressure and when Taylor was bundled over on the edge of the area, it gave Power then chance to set his sights. He duly did as, after the referee marched back the Town wall, he curled home a beauty and into the bottom left corner of Redmond's net.
Two added minutes was indicated by the Fourth Official before play restarted and these elapsed without further incident so Power's late strike set up an intruiging second period.
HT: Imps 1 Mansfield 1
Both sides emerged unchanged for the start of the second half with the Imps restarting proceedings. And it wasn't long before the net was bulging again as, two minutes in, Jamie Taylor fired the Imps in front.
The striker's 12th of the season came after Boyce flicked on a Gray throw-in and after Redmond saved his initial effort, there was Taylor to follow up and fire in from six yards.
The action quickly switched to the other end though and after Fofana was penalised for a foul on Green five minutes later, the free-kick was only cleared as far as Louis Briscoe who controlled the ball with his chest before volleying superbly into the top corner to level the scores in spectacular fashion.
After this action-packed start to the second half things calmed down somewhat as the hour mark came and went until Dempster was cautioned for a late challenge on Taylor. Referee Mark Haywood let play continue before booking the defender with play ending with a free-kick to the Imps following a foul on Sheridan.
The stadium erupted again 20 minutes in as, after Taylor superbly got the better of his marker in his own half sprinted clear and although his goalbound effort was kept out by Redmond up in support was Alan Power who neatly finished for his second and City's third of a pulsating game.
With the crowd in full voice, skipper Gary Mills was dumped to the deck by Adam Murray as he prepared to pull the trigger with Redmond at full stretch to tip behind Power's free-kick as he went in search of a third. The resultant corner was headed a foot wide by Boyce.
Mansfield make the first change of the game in the 72nd minute with Jake Speight replacing Ben Hutchinson. Three minutes later a deflected Briscoe effort led to a corner which the Imps dealt with well before the offside flag gave City the chance to calm things down.
With nine minutes on the clock a long Gray throw was flicked behind for a corner by Geohaghon and although Power's delivery was intercepted the ball remained in the Town half and when another throw came in, Tom Miller saw his spectacular volley crash against the bar.
Matt Rhead replaced Lindon Meikle before the Stags won a corner and whem City cleared their lines Sheridan was caught in two minds as he sprinted forward with the home defence able to intercept his ball across to Power.
Vadaine Oliver for Adam Smith was the Imps' first switch as the clock showed 87 minutes played with his first touch seeing him head a Geohaghon throw behind for a corner which was hacked away by Gilbert.
Four additional minutes was indicated by the Fourth Official with a superb Fofana interception denying Green a sight of goal before Mills tripped his man for a Mansfield free-kick. When this was played into the mix Farman produced a superb save to deny Rhead but when the ball was played in again the City keeper had no chance as Rhead powered in a header from six yards out
City's reponse saw Power curl in a free-kick which Redmond claimed whilst the last chance of the game came from an Imps' throw-in and after Gray hurled the ball into the box, Oliver saw his goal bound header hacked off the line by Thompson.
FT: Imps 3 Mansfield 3
City: Paul Farman, Dan Gray, Andrew Boyce, Tom Miller, Peter Gilbert, Gary Mills, Mamadou Fofana, Jake Sheridan, Adam Smith, Alan Power, Jamie Taylor.
subs: Paul Robson, Vadaine Oliver (for Smith 87), Nicky Nicolau, Aristide Bassele, Colin Larkin, David Morgan, Jake Turner.
goals: Power (45, 65), Taylor (47)
Mansfield: Shane Redmond, John Thompson, John Dempster, Exodus Geohaghon, Lee Beevers, Chris Clements, Adam Murray, Louis Briscoe, Lindon Meikle, Matt Green, Ben Hutchinson.
subs: Ritchie Sutton, Luke Jones, Jake Speight (for Hutchinson 72), Nick Wright, Anthony Howell, Matt Rhead (for Meikle 85), Lee Stevenson,
goals: Green (21), Briscoe (53), Rhead (90+3)
bookings: Thompson (18), Dempster (63)
Referee: Mark Haywood
Assistants: Alfie Greenwood & Anthony Tankard
Fourth Official: Robert Atkin
Attendance: 4,414 (1,176 visiting supporters)