Peterborough pulled off a stoppage-time fightback to see off Derby 2-1 and claim a first Sky Bet Championship win of the season.
Darren Ferguson's comeback kings turned around the game with two goals in an astonishing 11 minutes of additional time at the Weston Homes Stadium.
They looked set to suffer a third consecutive defeat at the start of the new campaign when falling behind to Derby substitute Jack Stretton's first Rams goal in the 77th minute.
The 19 year-old – sent on early in the second half after Colin Kazim-Richards was stretched off with a serious leg injury – found the net with a ferocious half-volley after Posh failed to deal with Graeme Shinnie's corner.
But Posh, who fought back from 3-0 down to draw against Lincoln and win promotion from League One on the penultimate day of last season, had more heroics up their sleeves.
One of their own teenage talents unleashed from the bench – Harrison Burrows – was in the right place at the right time to tuck away Joe Ward's low cross from close range to bring Ferguson's men level in the first minute of time added on.
That set up a thrilling finale with both sides chasing a winner and it was Posh who hit the jackpot thanks to another of their substitutes.
Siriki Dembele was on hand to fire into the far corner from 15 yards after another Ward delivery intended for Burrows had been cut out by Rams man Nathan Byrne.
That completed a brilliant and breathless end to a game between two sides tipped to face a major fight for Championship survival.
It had taken a while to come to the boil with both goalkeepers only required to make one save apiece in a low-key first period.
County man Kelle Roos almost made a meal of the attempt he was required to deal with in the 33rd minute when prolific Posh frontman Jonson Clarke-Harris tried his luck from 25 yards.
A well-hit blast squirmed through the legs of Roos before the relieved Dutchman was able to grab the ball from behind his body.
Posh began the second period brightly with Jorge Grant forcing Roos into a full-stretch save from 25 yards before Derby lost Kazim-Richards following a challenge with Posh defender Frankie Kent.
That cloud came complete with a silver lining as replacement Stretton proved to be a lively spearhead following his introduction.
He was close to being picked out by a Shinnie pass after one rapid attacking raid before being millimetres away from converting a cut-back from fellow substitute Louie Sibley.
Stretton made no mistake when his big chance arrived as he seized on a Ravel Morrison header to blast past Posh keeper Christy Pym.
But Derby's cheers soon turned to tears as Posh came roaring back to register their first triumph since climbing back into the second tier.
