Left-back Andy Frampton had put the Bees ahead but John Thompson headed Forest level from Nicky Southall's centre, only for Pratley to strike.
The win leaves them ahead of second placed United on goal difference.
Port Vale, the Iron's opponents at Glanford Park next Saturday, moved up to third with a convincing 2-0 win over Rotherham United.
They are now level on points with the Iron, with United just edging them on goal difference.
Nathan Lowndes picked up a pass from Michael Cummins, turned his marker and curled his shot past keeper Neil Cutler from 20 yards, whilst Millers' defender Shaun Barker was sent off for a professional foul on Billy Paynter, who went on to head Vale's second goal deep in injury time.
Matt Fryatt netted the only goal in for Walsall in their 1-0 home win over Swindon at the Bescot Stadium. The England Under-19 star scored from a tight angle when Jorge Leitao headed on a pass from Kris Taylor. They now move up to sixth.
Pre-season promotion favourites Bristol City continued to struggle, drawing 0-0 at Ashton Gate with Colchester in a live televised encounter.
The U's had defender Wayne Brown sent off, but City failed to break them down.
Grant Smith, Bradley Orr, Steven Gillespie and Richard Keogh all missed good chances for City as they looked to press home their numerical advantage.
Kemi Izzet hit the bar for Colchester as they nearly sneaked it.
Whilst Yeovil finally picked up their first league win of the season, beating Hartlepool 1-0 at Victoria Park.
Yeovil won it when Argentinian striker Pablo Bastianini headed in Lee Johnson's free-kick, they are still bottom but level on points with Doncaster.