The Portuguese eclipsed Lionel Messi's double in Barcelona's 2-0 win at Real Zaragoza earlier in the day and helped restore Real's one-point lead over their arch rivals at the top of La Liga.
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Ronaldo is La Liga's top scorer with nine goals, including eight in his last three games in the competition.
"It's great to score four and help out but the main thing is the team," the winger said in a television interview.
"As the coach said the other day, we can't be too euphoric because there is still a long way to go in the season."
Although Real have yet to play any of their potential rivals, they are in the sort of devastating form that could end Barca's two-year grip on the title and next month's "Clasico" between the teams can gauge how far Mourinho's team have come.
Racing, down in 16th position, pulled one back in the 73rd when a shot by Papakouli Diop went in off Markus Rosenberg's back.
Valencia are fourth on 16 after they slipped to a second straight defeat, losing 2-1 at home to Real Mallorca in Saturday's late match.
Fresh from his two goals against FC Copenhagen in the Champions League on Wednesday, the Argentine broke the home side's stubborn resistance with a clinical finish in the 42nd minute.
Zaragoza's Leonardo Ponzio was shown a straight red card two minutes after the break when he appeared to catch Daniel Alves with a flailing arm before Messi took his tally to five in six league matches in the 66th.
