Both sides learnt before kickoff they were guaranteed a knockout stage place after the earlier draw between Wasps and Leinster in another pool, leaving a shootout for Pool Five spoils.
Instead of rising to the occasion at a sold-out Franklin's Gardens, it was impressive Racing who left their small band of blue and white flag-waving fans celebrating with a bonus-point win.
The hosts, who finished pool runners-up, now face a tough away trip, possibly to European champions Toulon or three-times winner Leinster. And the Saints contingent of England players would have done little to impress coaches Andy Farrell and Graham Rowntree with the Six Nations starting next month.
A physically combative Racing, who will welcome All Blacks flyhalf Dan Carter after the World Cup in a move that underlines the big-money lure of the Top 14, ran Northampton ragged with three tries in a five-minute spell either side of halftime, including two from Argentine wing Juan Imhoff.
"The 14-point swing after halftime won us the game. To be the only unbeaten team in the pool stage is pretty special," said Racing centre Jamie Roberts, scorer of his side's fourth try.
"It's a pleasure to play with this team at the moment."
Lacklustre Saints, reduced to 14 men for 10 minutes early on when England hooker Dylan Hartley was sin-binned for tackling while on the floor, produced little attacking spark but some resolute defence kept Racing away from their tryline until late in the first half.
The Parisians finally broke through when some good handling ended with lock Francois van der Merwe putting in Imhoff.
The wing added another 90 seconds into the second half after a loose ball was hacked forward following the break down of a Northampton attack and moments later when fullback Benjamin Lapeyre gleefully dived over.
George North's seventh try in Europe this season gave Saints a glimmer before the power of his Wales team mate Roberts brought Racing another score to confirm their dominance.
"We came up against a very good Racing team, who put pressure on us in our lineout and in our scrum so we didn't have too many attacking opportunities, particularly in the first half," lamented Saints coach Jim Mallinder.
"Then when we did we coughed up ball... and that's what happens against quality sides."
(Reporting by Justin Palmer, editing by Alan Baldwin)
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