For all their obvious recent improvement under Chris Boyd, Northampton Saints were handed a swift lesson in where Europe's top echelon sits as familiar Champions Cup contenders begin to emerge.
Northampton have been the bright spark of England's Premiership Rugby this season, leading the competition with four wins from five games.
Boyd's vision for attacking, running rugby has been embraced to the point most recognise Saints are again a club on the rise. But after a promising early run, Saints were stopped in their tracks at the competition's midway stage last weekend.
Leinster were always going to be a different beast to anyone Northampton had faced this season, and so it proved.
After competing well in the first half Saints ultimately crumbled in the second spell to a 43-16 home defeat in which they conceded seven tries in front of their Franklin's Gardens faithful.
James Lowe and Jamison Gibson-Park were in fine form for Leinster. Lowe, the former Chiefs wing and fringe All Black, pushed 50/50 passes at times but he was superb in the air and opened the scoring after a brilliant counter attack sparked by classy Ireland outside back Jordan Larmour, who starred from fullback.
Former Counties Manukau fullback Ahsee Tuala quickly responded for Saints – Matt Proctor giving the last pass for his try – but when Boyd's men were forced to chase the game they battled in the face of Leinster's typically suffocating defensive strength.
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It doesn't get any easier for Northampton next week as they travel to Dublin for the return match against Leinster, who along with Toulouse, Ulster and Exeter, have won all three games in Europe this season. Racing 92 and Munster, who drew in round one, also remain unbeaten.
Boyd will hope he can call on Owen Franks and England test lock Courtney Lawes, both of whom missed this match with injuries.
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With Saracens continuing to rest several leading figures as they focus on avoiding Premiership relegation following their salary cap punishment, Jerome Kaino's Toulouse shape as the other premier contender.
Talented French playmaker Romain Ntamack starred as Toulouse maintained their unbeaten European run with a 23-9 win over Montpellier.
Ntamack clearly enjoyed the extra time and space as he shifted out one spot to second five, scoring two tries to confirm the four-time European champion's title claims.
Toulouse are yet to fully click this season and, yet, their credentials are already clear.
Dave Rennie's Glasgow Warriors ensured they are well in contention after snatching a dramatic 27-24 win in France over Jono Gibbes' La Rochelle that lifted them to second in their tightly-contested pool.
Needing victory to stay in the European hunt, Glasgow stormed back from 18-6 down. Former Hurricanes flanker turned Warriors captain Callum Gibbins sparked the revival by crossing from a lineout maul. Kyle Steyn then scored the decisive try after collecting a cross-field kick from Scottish playmaker Adam Hastings and running 60 metres to score.
The loss leaves Victor Vito, Tawera Kerr-Barlow and La Rochelle winless after three games.
Glasgow must repeat the dose on La Rochelle at home next week to hold off Sale Sharks in their pool.
Former Tasman, Chiefs and Crusaders utility Tom Marshall showcased his stepping to boost Gloucester's chances with two tries in his side's 26-17 win over Bundee Aki's Connacht.
The bonus point victory, which snapped a five-match losing run, propels Gloucester to second in their pool behind Toulouse.
Charlie Ngatai crossed for one of Lyon's four tries from second-five as they hammered Kieran Crowley's Benetton 28-0.
Former Bay of Plenty wing Toby Arnold started on the wing for Lyon and Rudi Wolf came off the bench. The in-form French club leads the Top 14 standings and sits third in their European pool, three points adrift of Saints.
George Moala, starting in the midfield with Isaia Toeava, scored for Clermont as they compounded Bath's struggles with a 34-17 win. Loni Uhila and Fritz Lee started in the pack and Faifili Levave came off bench for Clermont, who sit one point behind pool leaders Ulster.
Matt Faddes got one over Francis Saili as a late penalty from Ulster halfback John Cooney secured his side a last-gasp 25-24 home win over Harlequins, the defeat leaving the London club needing a miracle to reach the knockouts.
Bryn Evans started at lock as Sale Sharks fell 22-20 at home to Exeter Chiefs in a match that featured one second half try Jono Ross.
Marty McKenzie, unwanted by New Zealand Super Rugby teams, kicked two conversions from first-five but he could be in for a long season after Ospreys fell 40-19 to glamour French club Racing 92.
Ospreys are firmly rooted at the bottom their pool after three straight defeats.
In the Challenge Cup, Pat Lam's Bristol Bears remain one of three unbeaten teams - Toulon and Leicester the others - after their 37-11 win over Stade Francais.
Charles Piutau continues to impress after scoring one try, making 23 carries and four offloads for Bristol.
Champions Cup results:
Ospreys 19-40 Racing 92
Munster 10-3 Saracens
Ulster 25-24 Harlequins
La Rochelle 24-27 Glasgow Warriors
Northampton Saints 16-43 Leinster
Lyon 28-0 Benetton
Toulouse 23-9 Montpellier
Gloucester 26-17 Connacht
Sale Sharks 20-22 Exeter Chiefs