Gary Johnson's play-off dream is over after Dexter Blackstock's last-minute winner at the City Ground.

The on-loan QPR striker's brilliant volley also gave Nottingham Forest's hopes of avoiding the drop a massive boost.

A pair of defensive howlers led to both first-half goals as the sides went in 1-1 at the break.

First Iain Turner fumbled a harmless cross to allow Ivan Sproule to score City's opener before Jamie McCombe's miskick allowed Rob Earnshaw to equalise for Forest.

City took the lead through a Dele Adebola header before Jamie McAllister was sent off in much-disputed circumstances that led to Joe Garner's equaliser.

And the momentum was with the hosts who won a breathless game with seconds to go thanks to Blackstock's magnificent strike.

Chris Cohen had the first shot after just 20 seconds but Adriano Basso was easily down to save.

Blackstock should have given the hosts the lead seconds later but somehow glanced Cohen's free-kick wide from five yards.

City's first chance came when Cole Skuse crossed from the left and Michael McIndoe's attempt at an overhead kick bounced just wide of the near post.

City took the lead on 13 minutes when a speculative cross from the left by Lee Johnson was missed by both visiting strikers but Turner fumbled the ball low down after colliding with a defender, leaving Sproule an open goal to tap into.

Turner needed treatment after the injury but the greater blow was surely to his pride.

Nicky Maynard then tried to lob Turner after a pass from McCombe but fired well over the top.

And City threatened again on 25 minutes when a long free-kick from Bradley Orr saw McCombe climb highest and head across goal but this time Turner pulled off a fine save, tipping the ball to safety.

And Smith's save was made even more valuable not long after when a mistake from McCombe led to Forest's equaliser on 32 minutes. The big centre-half failed to deal with a bouncing ball over the top and Earnshaw nipped in to control and finish past Basso.

Forest could have been ahead five minutes later when on-loan Spurs full back Chris Gunter collected a half-clearance on the edge of the City box and let fly with a left-footer that curled narrowly wide.

After the break McAllister was handed an early booking for a foul on Paul Anderson and, from the free kick driven in by Cohen, a combination of Basso and Orr cleared off the line.

City's next attack – the first for some considerable time – ended with Orr shooting from range and Maynard so nearly deflecting the ball past Turner.

Then Lee Johnson's chip found McAllister bursting into the box but he volleyed wide of the near post when he should have hit the target.

And Sproule almost had his second when he won a foot race with keeper Turner but, from a tight angle, his shot lacked power and was cleared off the line by a defender for a corner.

Sproule was proving a threat. He got in down the right again but McIndoe just failed to turn in his low cross.

Then intelligent link up play between McIndoe and sub Gavin Williams saw the latter shoot from an acute angle and force a decent save from Turner.

City's improved play paid dividends on 78 minutes when Turner came for a hopeful long ball into the box from McAllister and got nowhere near it as Adebola climbed highest to glance a header over him and into the net.

But McAllister's day took a turn for the worse when he was sent off on 83 minutes. Adriano Basso had needed treatment so Forest threw the ball back towards City's goal but not out of play.

Gunter challenged for it and McAllister fouled him and was sent off for a second booking. From the set piece swung into the near post, Garner headed past Basso to send the home fans wild.

And there was more Nottinghamshire joy as Blackstock, who had previously been anonymous, netted the winner.

Nottingham Forest (4-4-2): Turner; Gunter, Wilson, Morgan, Lynch; Anderson, Perch (McGugan 80), Moussi (McCleary 61), Cohen; Earnshaw (Garner 71), Blackstock. Subs not used: Smith, Chambers.

Bristol City (4-4-2): Basso; Orr, McCombe, Fontaine (Iriekpen 46), McAllister; Sproule, Skuse (Elliott 66), Johnson (Williams 66), McIndoe; Maynard, Adebola. Subs not used: Henderson, John.