Tigers won the extremely rare shootout 7-6 and Roberts has not forgotten.
Racing, like Cardiff six years ago, have advanced through the pool stage of this year's revamped top-tier competition -- the European Champions Cup -- unbeaten to underline they are serious contenders to dethrone holders and Top 14 rivals Toulon.
"To be the only unbeaten team in the pool stage is pretty special," Roberts said after the Parisians overwhelmed Northampton 32-8 at Franklin's Gardens on Saturday. Victory helped them top Pool 5 and secure top seeding for the last eight.
"I managed to do that with Cardiff in 2009 and lost on penalties in the semi-final against Leicester which is one of the worst memories of my career but it's kind of driving me in Europe this year.
"We have a glorious opportunity now. That experience motivates me hugely to go on and win the European Cup."
Racing will host Saracens in the quarter-finals.
"A home quarter-final. It's going to be a massive match," added Roberts who now heads home to be part of Wales' Six Nations build-up.
"To play at the Stade Colombes, it's not an easy place to win for away teams. We'll be a very tough team to beat there."
Such is the competition for places at Racing that even someone of Roberts' pedigree as a British and Irish Lion is not an automatic first choice.
A man of the match performance against Northampton, scoring Racing's fourth try from close range with a typically powerful surge, should help his cause, however.
"I thought I was playing good rugby with Wales in November but it's been a bit of a strange one... I've gone back to Racing and only played twice before (the Northampton game).
"It kind of works like that in France -- the squads are so big. You find yourself playing one game and then you might not play for two or three weeks.
"It's been a little bit frustrating but as a player with aspirations you want to play in big matches for your club."
(Reporting by Justin Palmer; editing by Toby Davis)
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