The Scarlets and Racing Metro 92 lead the way after a 26-26 draw in west Wales, but last season's Heineken Cup runners-up, ASM Clermont Auvergne, are breathing down their necks after extending their unbeaten home run to 65 games against Harlequins.
The stalemate at Parc y Scarlets ensured the Welsh region cling onto pole position on six points thanks to tries scored. Racing Metro, who almost snatched a last-gasp victory, are just two tries adrift of the early pacesetters.
A relieved Scarlets coach, Simon Easterby, now has to face a double dose of Top 14 opposition in December with back-to-back games against Clermont. The two sides have met four times before in the Heineken Cup and the Scarlets have yet to win.
Clermont scored three tries and 20 points in the opening 25 minutes of their game with Harlequins, but only won 23-16 in the end without a bonus point. It was a second defeat in a row for Quins, who travel to France once again in Round 3 to take on Racing.
The atmospheric Stade Vélodome in Marseille looks set for a 40,000 plus attendance for the Heineken Cup semi-final clash on Sunday, 27 April between reigning champions, Toulon - gunning for a fourth European final in five years - and Munster Rugby, who have reached a record 11th tournament semi-final.