Leon Legge netted his second injury-time leveller in as many games for Brentford to deny MK Dons, who had been 3-0 up at half-time, three points at Griffin Park as the home side snatched a 3-3 draw.
Brentford, booed off at the break, produced a stunning second-half performance to send the Dons, who had been looking to close the gap between themselves and third placed Sheffield Wednesday, back to Milton Keynes with just one point instead of three.
The half-time score suggested a comfortable win for the Dons whose class shone through time and time again in the first-half, but Brentford showed why they can never be written off as Alexander's double stirred the Griffin Park crowd into a frenzy as the Bees refused to give up on three points without a fight.
Both Darren Potter and Angelo Balanta netted in the space of two minutes to stun Brentford and open a 2-0 lead for the Dons inside seven minutes before former Bees striker Charlie MacDonald added a third before the break.
It seemed an impossible task to come back from three down but Brentford were left to once again thank Legge for an injury-time equaliser as the Dons were left almost with the feeling of defeat having seen their lead disappear.
Robinson was without the services of Luke Chadwick due to a one-match suspension which paved way for Balanta to start the final game of his loan spell from Queens Park Rangers.
Less than two minutes on the clock Adam Smith, already with two spectacular goals to his name this season, went on a trademark mazy run down the right flank to show Brentford the danger he possess as he cut inside and then pushed back wide before riffling a shot against the post and into the side netting.
It was just a hint of what was to come from the Dons as they blew their hosts away with a lightening start when they took the lead inside the fifth minute. Dean Bowditch, starting on the right of midfield where he has arguably played his best football since joining from Yeovil in the summer, had the ball in a wide position and spotted the unmarked Potter at the edge of the 'D'.
The controlling midfielder has only scored once - in the FA Cup - for the Dons despite an array of efforts virtually every game. Yet, the former Liverpool and Sheffield Wednesday man was in the perfect position to connect sweetly with Bowditch's pass and beat Richard Lee in goal.
The dream start for the Dons was made even better over a minute later when Balanta, having broken his ankle on the very ground last season, exorcised some ghosts as he picked up the ball in the left of the area, beat two defenders before picking out the bottom corner with his left boot.
At times it all appeared too easy for the men from MK1 as they showed a touch of class in their play and movement across the pitch. However, there were occasions where the two goal cushion proved a little comfortable and Stephen Gleeson was given a firm warning not to become too complacent when Marcus Bean's strong challenge deep inside the Dons' half allowed him to rob possession.
The experienced Bean was able to thread a great pass through to Gary Alexander, only for the striker to drag his shot wide of the post.
It is not often Gleeson is out-tackled in a game, but it happened again when Sam Saunders showed the fighting spirit that brought out the vocal fans in the home ends to snatch the ball from the feet of the Irishman and create a chance for the Bees.
There was some good play around the Dons' 18-yard box before Saunders' cross was headed wide by Leon Legg.
After the hosts had enjoyed a significant period of pressure, the Dons managed to get back on top in the game and Potter had chance to add further to the score line before the break when MacDonald's cross was played back out and Potter, in a similar position to where he scored, curled a shot into the arms of Richard Lee.
A Dons corner was quickly turned into a Brentford attack as half-time approached when Bean hassled the ball from Dean Lewington and released Myles Weston but a scything challenge from Smith brought an end to his run. Unfortunately for Dons, it was a caution that will result in him missing the Colchester game on Monday at stadiummk.
Any brief hope of regaining a foothold in the game for Brentford quickly disappeared when MacDonald, adored by the Bees fans for three years during his spell at Griffin Park, added to their woes by stretching the Dons' advantage to three goals.
Once again it was the run of Bowditch that caused havoc with the Bees' backline - although there appeared to be confusion when the assistant raised his flag, seemingly for a foul - and when his fizzed in cross found its way through to the six-yard box it was inevitable that MacDonald would stroke the ball home.
The 30-year-old striker refused to celebrate in front of his former fans, but they responded by joining the Dons supporters in clapping and singing his name.
Robinson's men started the second half as they left off, intent to secure an emphatic victory. Balanta and MacDonald combined down the left with MacDonald seeing his initial cross blocked he was able to find Jabo Ibehre at the second attempt but the forward headed over.
Seconds later Bowditch found himself unmarked in the box and was allowed to turn 180 degrees to shoot at Lee, who was able to turn the ball out for a corner.
At the other end Lewington was left angered by a decision to award a foul against him on Jonathan Douglas, the midfield appeared to use his experience to win the foul. Saunders lined up to take the free-kick in a dangerous central position from 20-yards yet the delivery went straight at David Martin.
Despite the deficit, the Bees still showed plenty of desire to find a way back into the game and in the 65th minute they were offered a lifeline. Saunders, the one bright light of Brentford's performance, lofted a ball into the box from a deep position.
The presence of Clayton Donaldson inside the six-yard box ensured Martin went diving one way, but the Bees substitute, who came on at half-time, nodded the ball down for Alexander to pull a goal back with a thumping finish from close range.
The goal gave Brentford a reason to believe they could still take points from the Dons, and they had every reason to have every confidence when Balanta was penalised for handling Saunders' corner and referee Gavin Ward pointed to the penalty spot.
Penalty duties were left to Alexander and the striker made no mistake as he sent Martin the wrong way as he converted into the right of the net.
The momentum had truly swung back in favour of the Bees with over a quarter of an hour still to go Alexander's doubled teed up a nervy ending for the Dons. Robinson introduced Daniel Powell and Shaun Williams in the closing stages to pack out the midfield in an attempt to stop Brentford breaching their backline.
Brentford's ability to play until the very final whistle paid dividends when, in the 90th minute, Saunders' free-kick from the right of the box was smashed onto the underside of the bar by Douglas and Legge was in the right place at the right time to follow up with the equaliser to bring the roof of Griffin Park.
Brentford: Lee, Bean, Eger, Saunders, Douglas, Weston (Forrester81), Logan (Dean 83), Bidwell, Oyeleke (Donaldson 45), Alexander, Legge.
Subs not used: Moore, Diagouraga.
Goals: Alexander 65, 74, Legge 90
MK Dons (4-2-3-1): Martin; Smith, Kouo-Doumbe, MacKenzie, Lewington (c); Gleeson, Potter; Bowditch (Powell 78), Ibehre, Balanta; MacDonald (Williams 78).
Subs not used: McLoughlin, Flanagan, O'Shea.
Booked: Smith, MacKenzie, Gleeson
Goals: Potter 4, Balanta 6, MacDonald 41
Referee: Gavin Ward (Surrey)
Attendance: 5,397 (420 away)