The livewire fly-half's monster drop goal ultimately proved the difference between two teams who threw everything at each other in Paris.
Smith mixed smart game management with his trademark attacking flair as Quins stole a fine bonus-point win at La Defense Arena.
Quins lost out 30-29 at Racing in January, but this time refused to be edged out. Smith bagged a 16-point haul, comprising a try, that drop goal and four conversions.
Andre Esterhuizen, Alex Dombrandt and Jack Walker also crossed for Billy Millard’s men.
Stuart Lancaster’s Racing side also ran in four converted scores, leaving Smith’s snap long-range drop goal to win the day, with the visitors holding out under pressure for the win at the death.
England’s starting fly-half berth is vacant in the wake of captain Owen Farrell’s decision to stand himself down from Six Nations selection.
Smith and George Ford will battle it out for first refusal on the No 10 shirt, and on this evidence the Quins man will be hard to keep out of the side.
England boss Steve Borthwick’s game plan will always revolve around tactical and territorial mastery, no matter how much he looks to expand after the World Cup.
Smith’s long-term task has always been to show he can match the best 10s when it comes to applying a tactical chokehold.
But Sunday's showing in Paris could go a long way to convincing the England hierarchy that he is ready for an extended Test run at 10.
Quins will head back to London on the Eurostar on Monday buoyed by another potent victory, off the back of their 36-3 win over Premiership leaders Sale.
The west Londoners will host European elite outfit Toulouse at The Stoop on Sunday, where another win would put them in a robust Champions Cup position.