Substitute Blayney handed the visitors the lead on a wet and windy night at Windsor Park when he miscontrolled a backpass and his clearance rebounded into the net off Arsenal's Marouane Chamakh.
Lucky break: Morocco's Marouane Chamakh celebrates after scoring against Northern Ireland
Blayney then partially redeemed himself by tipping a fierce Adil Hermach drive onto the bar and Patterson stepped up to force a draw after Josh McQuoid was fouled five minutes from time.
The equaliser will give manager Nigel Worthington reason for optimism after what seemed like being a dismal night. The value of the exercise had been brought into question after 12 players withdrew from the initial squad named last week for a variety of reasons.
Worthington was forced to make eight changes from the side which laboured to a draw in the Faroe Islands last month.
In-form West Brom winger Chris Brunt, playing in an advanced role, had the best of the early opportunities but failed to test the goalkeeper before being withdrawn at half-time.
Green machine: Northern Ireland's Chris Brunt (right) skips past Morocco's Adil Hermach
Preston midfielder Adam Barton, who is also eligible for England, was handed a debut from the start by Worthington in the hope he could be persuaded to pledge his allegiance full-time.
Inverness' Jonny Tuffey was the initial pick in goal in the absence of veteran Maik Taylor and his status as second choice was only enhanced by what followed just 10 minutes after he left the action.
After torrential rain throughout the day, the pitch was heavy but Brunt attempted to make a bright start as he won possession from the kick-off.
Brunt broke forward and fed John Gorman out wide but the Wolves man's cross was easily claimed by Nadir Lamyaghri.
Brunt, recently linked with Liverpool after a fine start to the season, was intent on impressing but shot well over when a chance opened up from distance.
Morocco attacked down the flanks and Chakib Benzoukane cut inside from the left to force Tuffey to concede a corner. Aaron Hughes headed away from the set-piece but Kharja Houssine fired a shot back in which flew over the bar.
Brunt tried his luck from a 40-yard free-kick but again missed the target and Morocco began to show some neat attacking touches.
No holding back: Northern Ireland's Ryan McGivern (right) tackles Morocco's Younes Belhanda
Houssine had a shot blocked after being fed by Chamakh and Chadli put a good chance over on the rebound.
Northern Ireland survived a scare midway through the first half as Younes Belhanda slipped Youssef Hadji into the box but the Nancy midfielder shot straight at Tuffey.
Brunt showed more good touches as the hosts built a patient attack but was again off-target with his shot. Morocco came forward again with Chadli showing good skill on the left but captain Hughes headed behind.
Northern Ireland made four changes for the start of the second half, with Worthington bringing off Premier League pair Hughes and Brunt as expected.
Pat McCourt, one of the more influential players, was also forced off with a dead leg and Linfield's Blayney was also introduced.
Michael O'Connor, McQuoid and Rory McArdle were the other players to come on.
O'Connor quickly got in the action as he flashed a free-kick wide but two of the others may have wished they stayed on the bench.
McArdle played Blayney into trouble with a back pass which the Linfield keeper failed to control.
He hastily tried to kick away as Chamakh advanced but the Arsenal striker was too quick and his clearance rebounded off the Moroccan and into the net.
Morocco went close to a second moments later as Hermach unleashed a ferocious 40-yard drive but Blayney made some amends for his gaffe his he tipped onto the bar.
The visitors came forward again and Youssef Hadji shot wide from the edge of the area.
The game appeared to be winding down when Bournemouth forward McQuoid won a penalty from a corner after being pulled down by Rachid Soulaimani.
Plymouth's Patterson held his nerve to score from the penalty spot.
Morocco had a late chance to snatch victory but Youssef El-Arabi shot over after a weaving run.
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Explore more:People: Marouane Chamakh, Maik Taylor, Nigel Worthington, John Gorman Places: Liverpool, Morocco, Northern Ireland, United Kingdom