O'Connell stays level headed after victory.
The victory saw the Irish province complete their group campaign with a perfect six out of six wins for the first time in their history and move to 25 points - one ahead of champions Leinster in the race for top quarter-final seedings.
"It was a very good performance, especially when you consider how much pressure we were under at the scrum," O'Connell said.
"That has been coming for a while. We've been very close and it was very satisfying to see the back line finishing off a few moves. It's right up there because it came against a good side away from home at the business end of the Heineken Cup.
"At times we have showed some good form. The work ethic has been there and I was very happy to see the backs finishing off some moves.
"That 10-minute period just after half time gave us a real lift. To be under such pressure in the scrum and still come out on top is testament to the strength and heart of the team.
"Last year didn't go our way, but we've had a bit of luck along the way this season and worked very hard to go six from six. We've still got a bit of a way to go to get up to the standard of Toulouse and Leinster.
"We've proved nothing yet - we've just come out of our pool and won nothing. We've got a long way to go to emulate the teams of 2006 and 2008 who won the tournament."
Northampton coach Jim Mallinder was scathing about his side, saying: "They looked after the ball and we gave it away."