Morecambe goalkeeper Barry Roche scored a last-minute equaliser to end The Shrimps’ losing run in dramatic fashion.
The popular stopper went up for a 94th minute corner and rose highest to nod in Shaun Miller’s centre to set off scenes of pandemonium at the Globe Arena.
Gareth Evans’ first-half goal had looked like condemning The Shrimps to a fourth straight defeat but Jim Bentley’s side pushed for a leveller before the remarkable conclusion.
Both sides made an enterprising start at the Globe Arena but the closest either team came was a wind-assisted Barry Roche clearance that nearly caught out opposing goalkeeper Ryan Fulton on the quarter hour.
Doing his more regular job Roche had no trouble in keeping out Michael Smith’s deflected shot after an Enda Stevens free-kick found its way into his path.
Roche was then beaten by Adam Webster’s volley from Naismith’s corner on 28 minutes but Kevin Ellison was in the right place to clear off the line.
Despite some promising attacking play The Shrimps were having to settle for half chances, Jamie Devitt seeing a well-struck free-kick held by Fulton 10 minutes before the interval.
Devitt was nearly the villain shortly after but Marc McNulty could only blaze over when free in the area after the Irishman had been robbed of possession 30 yards from his own goal.
The game continued to go from end-to-end with Tom Barkhuizen testing Fulton before the visitors got their noses in front five minutes before the break.
Naismith strode unchallenged through The Shrimps half and fed Evans in on the right side of the box and he made no mistake, finishing low beyond Roche.
It was nearly two for the visitors on the stroke of half-time but Smith saw his sweetly-struck strike fizz past the post as Pompey broke with menace.
Having nearly scored an unlikely goal with the help of the breeze Roche was nearly beaten by it early in the second half, Ben Close’s corner hitting the top of the crossbar.
The second half was a more cagey affair though with chances at a premium.
Luke Conlan, who had a fine game at left back for the hosts, saw two crosses flash agonisingly across the face of goal while Devitt’s chipped effort hit the roof of the net.
Lee Molyneux saw a shot saved in the 93rd minute and that looked like it was that for The Shrimps.
It was far from it however as Roche charged forward for the corner, rising to head home Miller’s corner to become the hero of the hour.
Morecambe: Roche, Beeley (capt), Dugdale, Parrish, Conlan, Goodall, Fleming, Barkhuizen, Devitt (Molyneux 82), Ellison (Mullin 75), Miller. Subs not used: O’Hara, Edwards, Wilson, Doyle.
Booked: Fleming, Beeley
Portsmouth: Fulton, Davies, Webster, Clarke, Stevens, Close, Doyle (capt), Evans, McNulty (McGurk 83), Naismith (Bennett 72), Smith (Roberts 72). Subs not used: Bass, Burgess, Barton, Chaplin.
Referee: Richard Clark.
Attendance: 1,399 (479 away)