But a third Pool victory took them back to the top of Pool 3 and set-up a fantastic final round clash with Bristol on Sunday.
Thanks to the 19-11 home win over Bristol that French champions Stade Français Paris recorded on the weekend, there will be three teams fighting for the right to reach the last eight next weekend.
The Blues, who head the Pool with 16 points, are guaranteed a ticket into the quarter-finals if they win or draw. They could also qualify as Pool winners if they get two losing bonus points.
But both Bristol or Stade could also pip them to the top spot. For Bristol to reach the last eight for the first time they need to beat the Blues, stop their visitors from getting a bonus point and hope Harlequins can beat Stade.
For the French champions to progress they will need to secure either four or five points at the Twickenham Stoop. They will only need four to go through if Bristol beat the Blues without either side getting a bonus point, or need five if Bristol come up with a bonus point in winning their last game and stopping the Blues from taking a bonus point.
"Going to Bristol was always going to be difficult for us and this win over Harlequins hasn't changed anything. But the good thing is that our destiny is in our own hands," said Young.
"I think Bristol will start as favourites because they are playing at home and all the pressure is going to be on them because they will need to go for the bonus point as well as the victory.
"Sure, there is going to be pressure on us to finally make it through to the quarter-finals of the Heineken Cup having put ourselves in this position and topping the Pool going into the last round of matches.
"But that is a nice kind of pressure - the kind of pressure that you want as players and coaches. We want to be in the big competitions and it would be great if the Blues could finally qualify for the last eight of the Heineken Cup."
Blues skipper Xavier Rush was named Heineken man of the Match for his inspirational performance and he can't wait for Round 6.
"There are still three teams in the hunt and that is going to make for a great final weekend," said Rush.
"It is all going to come down to the last game for us and that's the way it should be in a competition of this quality. We know Bristol is a difficult place to go and win, but we are looking forward to the challenge. It's going to be a hell of a game."