There was also an historic first in Durban where Sharks became the first South African franchise to take part in the new-format Champions Cup, edging English side Harlequins 39-31 in a pulsating match.
The Cape Town-based Stormers looked as though they were also going to open with a win as they went in at half-time with a 14-3 lead at Clermont. But the Top 14 side ran in two tries in the second half, scoring 21 points without return to win 24-14.
Racing, laced with international stars including Scotland fly-half Finn Russell and France centre Gael Fickou, went into the tournament with high hopes of improving on last season when they lost to eventual champions La Rochelle in the semi-finals.
But, transported from their usual home in Paris because of a rap concert already scheduled at their La Defense Arena, they were helpless from the start against the Irish marauders, who lost to La Rochelle in the final last May.
Prop Andrew Porter crashed over in the fourth minute and tries from Dan Sheehan and Garry Ringrose, while Racing were down to 14 men after hooker Camille Chat was shown a yellow card, gave Leinster a 21-3 lead at the break.
Further tries from World Player of the Year Josh van der Flier, who scored twice, and Ed Byrne, sealed the thrashing - and the bonus point. former England wing Christian Wade's try was the only consolation for the French.
"I don't know if it was a show of force," said Leinster coach Leo Cullen.
"We wanted to get this competition off to a good start. With this format, you don't have too much room for error, you have to maximise each of our points.
"It was not easy, Racing were always dangerous. We did well to score quickly because Racing tend to scoring often and quickly. Taking that away from them helped us a lot.
"But we were never comfortable, they pose such problems."
Shark attack
Defending champions La Rochelle eased to a 46-12 win over Northampton, racing to a 32-0 by half-time with tries from Brice Dulin, Pierre Bougarit, Pierre Boudehent and Dillyn Leyds.
Gregory Alldritt and Ulupano Seuteni added second-half tries.
At King's Park in Durban, Harlequins outscored a Sharks side including eight internationals, including Springbok captain Siya Kolisi, five tries to four but still lost. A small consolation was that both sides took a bonus point for tries scored.
Josh Bassett put the Premiership side ahead in the seventh minute but Bongi Mbonambi struck back and two tries from Springbok wing Makazole Mapimpi took Sharks into a 22-7 lead.
Will Evans reduced the lead with Quins' second try but Werner Kok sprinted away for a superb solo try and Curwin Bosch added a penalty to make it 32-14 for Sharks.
Quins rallied gamely. Andre Esterhuizen, who played for the Sharks until moving to London in 2020, dotted down twice and Bassett added his second to reduce the deficit to a single point with two minutes remaining.
Sharks closed the deal, though, with Boeta Chamberlain completing a fine move down the right.
Stormers made the early running at Clermont, flanker Deon Fourie's try off a line-out close to the line giving them the edge in the first half.
Clermont were a different proposition in the second half. Tries from Alex Newsome and Aliverati Raka gave them the lead and the boot of former France fly-half Jules Plisson - a drop goal and a penalty - settled the outcome.
Bulls saw off last season's European Challenge Cup winners Lyon 42-36 in Pretoria scoring six tries, from Sibongile Novuka, Bernard van der Linde (2), Nizaam Carr, Stravino Jacobs and Chris Smith.
Lyon had trailed by 16 points at one stage but the South Africans held their nerve.
