Connacht put their recent struggles behind them to produce a phenomenal performance at the Stade Ernest Wallon, the home of the four-time Heineken Cup champions.
Perfect conditions allowed both sides to play expansive rugby and provided a tense and thrilling clash for the 16,742 supporters in attendance.
The traveling Connacht support erupted in the North Stand when Dan Parks gave Connacht the lead with a 13th minute penalty. The experienced out-half then added a sweetly-struck drop goal two minutes later to make it 6-0.
His opposite number Jean-Pascal Barraque missed his first shot at goal on 30 minutes, but he make up for his first mistake with a brilliant individual try on the stroke of half-time.
The French side had been working hard to prise open the Connacht defence and eventually found a gap with just a minute to go in the first half. Barraque touched down at the posts for a try which he converted made it 7-6 to the home side at the break.
It was a lead Guy Noves' men had done little to merit and a well-struck penalty from Parks, five minutes into the second half, saw the visitors swiftly retake the lead.
Just two minutes later, livewire scrum half Kieran Marmion's heroic efforts were rewarded when the 21-year-old’s pass gave backs David McSharry, Robbie Henshaw and Fionn Carr the space to make huge yards up the right wing.
Carr was halted just short of the whitewash but with the support of Jake Heenan and Eoin McKeon coming in, Marmion was there to burrow over for the try. Parks added the extras for a 16-7 scoreline.
It would inevitably prove to be a hard slog and a huge test of the resolve of this Connacht squad, who had won only two games this season before the journey south to France - with both victories coming against Zebre.
When Barraque missed his second penalty of the night, Toulouse boss Noves moved to introduce Lionel Beauxis into the game for the final quarter.
An electrifying attack came just before the hour mark when Toulouse lost the ball in the Connacht 22. A Marmion pass found replacement winger Gavin Duffy who offloaded under huge pressure to the onrushing Henshaw.
The hugely influential full-back was sent racing clear and touched down under the posts. But referee Marius Mitrea asked TMO Alan Falzone to check the origin of the move. An apparent knock-on some 70 metres back in the play ruled out the try.
Connacht were in no mood to just try and defend for the remainder, with the fresh legs from the bench helping them to maintain a high intensity in both attack and defence.
A converted try from captain Thierry Dusautoir brought the margin down to two points with just 15 minutes remaining, putting the pressure back on Connacht.
They handled it remarkably well, coping with some frustrating decisions from the match officials and the noise generated by the partizan home crowd.
The lusty voices of the travelling support also willed Connacht on with a couple of well-timed renditions of 'The Fields of Athenry', and players like tireless flanker Heenan, McSharry, Eoin Griffin, Denis Buckley and Michael Kearney really came of age in the French fortress.
It all amounted to a massive 'squad effort', commanded by Kiwi captain Craig Clarke, and although Parks missed with a drop goal effort and a subsequent long range penalty attempt, the disciplined defensive wall of white and blue gave no quarter as Toulouse saw out the match battering into tackles around the halfway line.
Referee Mitrea's final whistle sparked wild celebrations on the pitch and in the stands as Connacht - heroes from 1 to 23 - savoured the biggest result in the province's long history.
This shock victory has seen Lam's history makers etch their names into Irish rugby and Heineken Cup folklore and means they are still in the running to reach the quarter-finals, lying a point behind Toulouse but level with second-placed Saracens.
They will also be fiercely determined to show this was not a one-off display with Toulouse making the trip to Galway next Saturday.
A mention must go to Connacht stalwarts Duffy, Michael Swift, John Muldoon and Brett Wilkinson who all played their part, as the province became the first team to win here in the Heineken Cup since a Parks-inspired Glasgow Warriors side in January 2009.