Saracens' European Rugby Champions Cup defence started with a comprehensive defeat at Racing 92, while Dan Biggar kicked Northampton Saints to victory over Top 14 high-flyers Lyon on Sunday.
Sarries, who are reportedly not going to appeal against a 35-point domestic deduction for an alleged breach of salary cap rules, missed the quality of their England contingent still yet to return from Rugby World Cup duty in a 30-10 defeat in Paris.
Virimi Vakatawa broke through a gap in just the ninth minute to get Racing underway and Teddy Thomas, fresh off a hat-trick in last week's 25-9 beating of Stade Francais, squirmed over to stretch the lead.
Alex Lozowski finished for Saracens early in the second half after Nick Tompkins stole the ball when Finn Russell knocked on but the Scotland fly-half quickly made amends with a wonderful jinking try and Wenceslas Lauret completed a convincing Pool 4 success.
Biggar was making his first appearance since suffering World Cup semi-final heartache with Wales and was in fine form with the boot as Northampton earned a potentially priceless Pool 1 win.
The fly-half kicked 20 points, including six penalties, in the 25-14 beating of Top 14 leaders Lyon, who were outclassed at Franklin's Gardens.
Rory Hutchinson scored Saints' only try in the first half and Lyon missed out on a losing bonus point despite two second-half scores from Thibaut Regard.
Rounding out the action, a depleted Connacht side earned a fine 23-20 victory over Montpellier in their first Champions Cup outing in three years.
Backs Tiernan O'Halloran and Kieran Marmion were absent for the clash, as were big hitters Paddy McAllister, Finlay Bealham, Quinn Roux, Gavin Thornbury and Sean O'Brien in the forwards.
However, tries from Paul Boyle, stand-in captain Tom McCartney and Caolin Blade helped Connacht start their Pool 5 campaign with a win at the Sportsground.