Lucu boots Bordeaux-Begles into Top 14 semis
Lucu's efforts set-up next Saturday's last four game with 14-time winners Stade Francais at Bordeaux's 42,000-capacity football stadium.
"We felt a lot of pressure during the week. We managed to score when we needed to," captain Lucu told Canal+.
"We had the semi in Bordeaux in our mind. The season's been long, now we have to recover because there's a big game against Stade Francais ahead of us."
In the other semi held on Friday at the same ground, Toulouse, champions on a record 22 occasions, face La Rochelle in a repeat of last season's final.
Racing, with South Africa World Cup winner Siya Kolisi in their ranks and who have signed ex-England captain Owen Farrell for next season, were ill-disciplined.
The result means ex-South Africa captain Kolisi ends his first campaign in French club rugby trophyless.
More than 28,000 were present at Bordeaux-Begles' Stade Chaban-Delmas for the game.
The hosts led 14-9 after half an hour as Lucu slotted three penalties and Congolese winger Madosh Tambwe crossed with South African full-back Tristan Tedder replying with three shots at goals of his own.
Racing thought they were level five minutes later but Fijian winger Vinaya Habosi's superb solo try was chalked off by the video referee for a forward pass.
The game then turned in Bordeaux-Begles' favour as hooker Maxime Lamothe barrelled over from a rolling maul and club captain Lucu's conversion made it 21-12 at the break.
Lucu, who lost his place in France's starting lineup after a sluggish start to this year's Six Nations, then added a penalty and a conversion either side of full-back Romain Buros' 52nd minute try.
With 20 minutes to play Lucu moved across to fly-half to end the game before replacement Max Spring claimed a consolation try for Kolisi's side.
'Catastrophic'
Earlier, France fly-half Louis Carbonel kicked a late penalty to keep billionaire-backed Montpellier in the French Top 14 with a 20-18 victory at Grenoble the promotion play off.
Carbonel saved Montpellier's skin with a 77th minute effort after the outfit owned by Mohed Altrad trailed at the break.
Grenoble, whose budget is a third the size of their visitors, lost in the fixture for a second straight year.
"For us to be in this game is scandalous, we had a catastrophic season," Montpellier scrum-half Leo Coly told Canal+.
"Now I hope we'll use it as a lesson, and the club also because there are 23 players on the field, 40 in the squad and a whole club that are to blame," he added.