Harlequins are out on their own with 19 points after the opening four rounds of Pool action in the 18th Heineken Cup tournament - fellow four-from-four clubs ASM Clermont Auvergne and Toulon both on 18 points.
The race for quarter-final qualification will enter the final straight in the New Year when the tournament resumes with the four best group winners earning the invaluable advantage of being home in the prestigious and lucrative last eight.
Round 3 produced plenty of surprises but English flag bearers Harlequins had little trouble in doing the double over tournament newcomers Zebre with a 53-3 bonus point win at the Twickenham Stoop.
They face Connacht Rugby at home in Round 5 knowing that they are just one match point away from guaranteeing their quarter-final place before finishing the Pool stages with a trip to Biarritz Olympique, whom they lead by 10 points.
"People say we are stuttering along but we have won 13 out of 16 in all competitions - and we are unbeaten in Europe," said Quins Director of Rugby Conor O'Shea.
"When I stopped counting against Zebre the penalty count was 24-4 in our favour.
"And that was the fourth game in a row that sides have conceded 20 penalties against us and it shows what teams are trying to do to stop us playing."
Nevertheless Quins still managed seven tries with All Blacks outside half Nick Evans contributing 18 points with the boot.
