Prop Tau Filise and wing Alex Cuthbert went over for Blues tries with Dan Parks kicking 16 points.
Racing's Juan Imhoff went over while Gaetan Germain kicked 12 points and Juan Martin Hernandez a drop-goal.
Roberts' World Cup skipper Warburton was making his return at Stade Yves Du Manoir following his sending off in the 9-8 semi-final defeat by France, alongside prop Gethin Jenkins, lock Bradley Davies and scrum-half Lloyd Williams.
Racing were without four front-line players and despite an early advantage at the scrum, they were unable to overcome the Blues' tenacious approach in defence.
The visitors were also more than a match for the French club in attack, gaining due reward with their two first-half tries.
Down's injury clearly unsettled the visitors and Germain kicked a penalty as the side coached by Justin Burnell and Gareth Baber regained their composure.
There was also a memorable drop-goal from the boot of Argentine fly-half Hernandez.
However, when the Blues got into their stride, a try was soon forthcoming.
Had Down's replacement Paul Tito not been knocked into touch after a sweeping move, that touchdown would have come sooner.
But from the line-out the Blues stole the ball as a maul collapsed and it popped up to Tongan Filise who went over unopposed for Parks to convert.
Scottish international Parks and Germain continued their kicking duel and Hernandez's slick pass to Imhoff gave his fellow countryman the time and space to go on a mazy 50-metre run to the line.
Poor defence from Tom James - who was otherwise in excellent form - also helped Imhoff on his way to the line.
Full-back Chris Czekaj was also impressive in attack, particularly from deep, but it fell to Cuthbert to make the most of another opportunity as he squeezed in at the corner.
Parks converted magnificently from the touchline and the Blues led 17-14 at the break.
The kicking duel betwen Parks and Germain recommenced after the break with the visiting fly-half proving his credentials in that respect with three second-half penalties as the game continued on a knife-edge.
Racing's downfall was compounded by their indiscipline in defence where Irish referee George Clancy would not tolerate their regular forays into the offside zone.
That allowed Parks to keep his side ahead despite Germain's equally impressive goal-kicking display.
Gaetan Germain; Sereli Bobo, Henry Chavancy, Fabrice Estebanez, Juan Imhoff; Juan Martin Hernandez, Mathieu Loree; Andrea Lo Cicero, Benjamin Noirot, Juan Pablo Orlandi, Karim Ghezal, Jone Qovu Nailiko, John Leo'o, Antoine Batut, Jacques Cronje (capt).
Jonathan Wisniewski for Estebanez (47), Nicolas Durand for Loree (55), Eddy Ben Arous for Lo Cicero (70), Johannes Coetzee for Orlandi (55), Lionel Nallet for Ghezal (47), Remi Vaquiin for Leo'o (70).
Not Used: Thomas Bianchin, Virimi Vakatawa.
Chris Czekaj; Alex Cuthbert, Casey Laulala, Jamie Roberts, Tom James; Dan Parks, Lloyd Williams; Gethin Jenkins, T Rhys Thomas (capt), Taufa'ao Filise, Bradley Davies, James Down, Michael Paterson, Sam Warburton, Xavier Rush.
Paul Tito for Down (3), Gavin Evans for Roberts (17), Ceri Sweeney for Laulala (72), Scott Andrews for Filise (73), Andrius Pretorius for Rush (70),
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