Isa the hero as Blues grab a point
Montpellier 22 Leinster 16
This was the game that would give definitive information about where Leinster stand on their way back to the pinnacle of European rugby.
They all stood in line for a minute's round of applause in appreciation of the memory of Anthony Foley, wearing red jerseys backed by the number eight.
The first Montpellier scrum lasted ten seconds and Leinster never budged an inch.
The first Leinster lineout was taken in by Devin Toner and mauled without a gain.
The terms and conditions of engagement had been set on a heavy patch of mud.
It was noticeable how Jonathan Sexton looked to slow down the game. The closest either side came to points was when Francois Steyn's penalty clipped the outside of the left upright in the 21st minute.
It took a Sean O'Brien steal to relieve pressure and, two driving mauls later, Isa Nacewa, rather than Sexton, slotted a penalty for the lead in the 26th minute.
The returning O'Brien claimed another poach, only for Cian Healy to lose the ball forward in contact.
Vincent Martin scythed through from turnover ball for Steyn to make it 7-3 on the half-hour.
Heaslip's needless grab at Paul Willemse in the air at a lineout meant Montpellier were handed prime position.
From there, two long passes put giant wing Nemani Nadolo, literally, through Rob Kearney and Luke McGrath for Steyn's conversion to rub salt into the wound for 14-3 at the interval.
It looked even more worrying when Sexton and O'Brien failed to emerge for the second half.
Joey Carbery stepped up as the main playmaker and Jordi Murphy stepped into the back row.
It wasn't too long before Mick Kearney was forced off for a Head Injury Assessment.
Referee Luke Pearce took the view Leinster were guilty of twisting the scrum illegally. Steyn made them pay from straight in front of the sticks in the 47th minute.
Half-backs Carbery and McGrath each had a pop at the fringes and Jack McGrath's clash of heads with Jannie du Plessis resulted in the latter leaving due to concussion.
A period of keep ball was too much of a temptation as Montpellier's defence drifted offside and Nacewa struck for three points in the 53rd minute.
Leinster had every right to feel aggrieved when Kearney was binned for Joffrey Michel's milking of a penalty as the Frenchman made no attempt to evade the stationary full-back.
The Blues did extremely well to neutralise a maul for the reward of a scrum.
Heaslip's pick-up off the rear was picked off by Nadolo's smart interception for the try which stretched the gap to 16 points.
Lock Willemse's rash decision to take out McGrath allowed Nacewa to land his third penalty.
Centre Garry Ringrose traversed the pitch, cutting back inside Willemse for a clean break that was halted by a lack of support.
There was still the opportunity for a losing bonus-point for Leinster if they could breach the home defence.
Ringrose was immense in hammering out a hit and recovering the loose ball to set an attack in motion.
The composure of Carbery and angles onto the ball of Heaslip were undone, with the compensation of a lineout.
The maul moved forward. Dan Leavy almost made it and Jamison Gibson-Park twice sniped to within a metre
The influence of Leavy carried impact, Carbery was measured in his distribution and Gibson-Park's cut-out pass put Nacewa in for a well-deserved try.
Crucially, the captain had the presence of mind to make a beeline inwards from the corner flag.
He converted to enable Leinster to lead Pool Four by their losing bonus-point.