Full time: Nottingham Forest 2 Vs Sheffield Wed' 1
The striker netted once in each half to help Billy Davies' side respond to seeing their 19 match unbeaten run brought to an end at Derby last weekend by claiming three valuable points at the City Ground.
Alan Irvine, who was named manager of the month prior to kick-off, might have thought his side had done enough to earn a point after seeing on-loan Derby striker Luke Varney equalise in the 73rd minute.
But Blackstock followed up his 24th minute penalty with a bundled second ten minutes from the end to get Forest's promotion push back on track.
Forest took a 1-0 lead into half-time but only after taking some time to break down the stubborn resistance of a hard working Wednesday side.
The breakthrough came in the 24th minute, when Wednesday finally handed Forest an opportunity on a plate.
The visitors had worked hard to close Forest down and deny them space in the opening exchanges, but the desire to shut out a shot from Dexter Blackstock, just inside the box, saw Darren Purse punished for a handball as he raised his arms to block.
And Blackstock was decisive from the spot, powering an emphatic finish high to the left of keeper Lee Grant.
It had been Forest's first meaningful effort on goal – but they were sparked into life by taking the lead.
Nathan Tyson forced a smart save from Grant with a low, driven effort from 25 yards, while Robert Earnshaw saw the keeper get across goal quickly to punch away his precise, bending free-kick.
Wednesday's best opportunity had fallen to Luke Varney, the on-loan Derby man, but the striker hesitated too long and allowed Kelvin Wilson to slide into block his angled shot.
It was the visitors who almost drew first blood after the break as midfielder Darren Potter's free-kick took a deflection off the Forest wall that saw it loop onto the bar and bounce away to safety.
Cohen saw a shot deflected wide at the other end, when it looked as though the Wednesday defence would open up for him.
While full back Frank Simek saw a rising effort fly narrowly wide of the post for the Owls, after advancing forwards down the flank.
A double change revived Wednesday, with substitute Etienne Esajas playing a key role, feeding the ball into the box for Varney to pounce, firing a powerful finish into the corner from 12 yards.
But Forest responded to take the lead again, as a Cohen free-kick caused chaos in the six-yard box, with Blackstock forcing a reaction save from Grant, before firing home the rebound from close range.
FOREST: Camp, Gunter, Morgan, Wilson, Perch, Cohen, McKenna, Moussi, Tyson, Blackstock, Earnshaw. Subs: Smith, Chambers, Anderson, McGugan, Adebola, McGoldrick, Majewski.
WEDNESDAY: Grant, Spurr, Purse, Tudgay, Potter, Beevers, O'Connor, Varney, Simek, Soares, Gray. Subs: Hinds, McAllister, Esajas, Lekaj, Clarke, Boden,. Jameson.
REFEREE: Trevor Kettle
Nottingham Forest's Dexter Blackstock

Comment on this story