Pompey were denied a return to the top of League Two at the death as Stevenage broke their hearts.
The hosts were on track for a 1-0 victory as the game entered five minutes of stoppage time.
Then Charlie Lee hurled in a throw-in from the right and substitute Brett Williams’ header looped over Aaron McCarey to net a cruel, cruel leveller.
Up until that point, Fratton Park lucky omen Conor Chaplin had popped up to conjure up the magic which appeared to have given the Blues a much-required victory on home soil.
Although Teddy Sheringham’s side could not be accused of operating with a defensive priority, at that stage the Blues were still struggling to break them down.
Then Chaplin was called off the bench in the 71st minute in place of Rommy Boco.
The diminutive forward’s previous four goals this season had all arrived at Fratton Park.
And he repeated his favourite trick by drilling home a left-foot shot six minutes after entering the field.
It was the perfect entrance at a time when frustration was creeping in among the 14,900 who had previously seen only two league wins on home soil.
Yet it was Williams who would have the final say to shock the Fratton faithful and send the visiting players and their supporters wild.
In the process, it prevented Pompey returning to the top of League Two, after Oxford’s victory over leaders Plymouth.
As it was, it was a very quiet Fratton Park once the final whistle had died out.
Pompey’s boss made the one change to the side which won at Newport County at the weekend, with Boco coming in for Kal Naismith on the right of the attacking three, having made his Blues debut as a substitute at Rodney Parade.
With Naismith dropping to the bench, that was also the only change among the substitutes, with last week’s loan recruit from Sheffield Wednesday Caolan Lavery among them.
Elsewhere in the side, Aaron McCarey was facing the final appearance of his initial 28-day loan from Wolves.
And Adam Webster continued at centre-back in place of Matt Clarke, having been granted his first league start of the campaign in the 1-0 victory at Newport.
Barely 50 seconds after kick-off, McCarey was forced to pluck Tom Pett’s deft cross from the left out of the air from a dangerous position.
At the other end, Gary Roberts drilled in a left-foot shot which keeper Jesse Joronen comfortably saved low down.
On four minutes, Boco tried his luck with a skidding left-foot shot which had Joronen pushing the ball behind.
The resulting corner was taken by Kyle Bennett, yet his attempt to pull the ball back found a Stevenage player and the visitors cleared easily.
Moments later the Fratton end embarked on a chorus of ‘Oh Teddy, Teddy’ a gesture appreciated by Stevenage’s boss, who made a point of applauding the supporters.
The visitors played some attractive football and a fine flowing move on 13 minutes from Dipo Akinyemi forced Webster to intervene with a flying headed clearance.
Then Pett drove in a cross from the right which flashed across Pompey’s goal, before Armand Gnanduillet headed wide at the far post.
Sheringham’s men had started the brighter and when Gnanduillet was well tackled by Adam Barton, Pett drove the loose ball well over the crossbar and into the Fratton end.
Pompey’s responded as Christian Burgess found Ben Davies down the right with a marvellous pass from his own half and the right-back’s left-foot cross was met by a Boco header, which was easily taken.
The Blues then had appeals for a penalty waved away when Jerome Okimo appeared to catch Davies’ foot as he shaped up to cross from inside the box, leaving the right-back with his arms outstretched in disbelief as he sat on the Fratton turf.
Davies was proving influential and his next contribution was a superb cross from the right at the end of a twisting and turning run, only for Matt Tubbs to fail to get enough on it with a header.
Pompey should have taken the lead, however, in the 32nd minute after Mark Hughes’ slip had let in Tubbs down the right-hand side.
The striker drilled in a cross which Bennett flicked into the path of Roberts, who fired his shot straight into the side-netting when he should have done better.
The match was proving an open affair and when Roberts sent in a deep cross, Boco popped up at the far post with a volley back across goal which Tubbs couldn’t quite get under control.
Stevenage should have broken the deadlock early in the second half after a wonderful move.
The visitors worked the ball through the Pompey defence, resulting in Akinyemi finding himself free inside the box from the angle, yet he drove his shot wide of the far post.
Pompey were also left cursing missed opportunities in the 52nd minute as the match remained goalless.
Roberts drove in a cross from the left which Tubbs somehow failed to connect with at the far post, although a Stevenage foot had taken a slight nick.
From the resulting corner delivered by Roberts, the ball fell for Bennett inside the box, yet he took a touch before curling a right-foot shot well over the bar.
Steady home pressure then resulted in Michael Doyle’s 59th minute thunderous left-foot shot from 25-yards brilliantly pushed around the post by Joronen.
Cook made his first change in the 61st minute when Lavery came on for Tubbs, also occupying the lone striking role in his 4-2-3-1 system.
Moments later, the loanee produced superb skill to control McCarey’s clearance and lay the ball into the path of Bennett, whose shot fizzed over the bar.
But on 77 minutes the Blues took the lead, with Webster the instigator.
The central defender strode forward with the ball and pushed it down the left channel in the direction of Chaplin, with Jamie McCombe missing it.
Suddenly Chaplin was free and he drove in a left-foot shot which beat Joronen at his near post as Fratton Park erupted.
Finally the hosts had their noses in front and Chaplin almost added another five minutes from time when he drove a left-foot shot agonisingly wide of the far post.
The fourth official indicated five minutes of time added on and Stevenage stunned the home crowd when Williams struck with his header.
It meant Pompey were denied the victory – and top spot.