La Rochelle booked a Top 14 semi-final trip to Toulouse after holding off a late fightback to win 19-13 at Racing 92.
Racing finished the regular season in fourth, a place ahead of their opponents, yet they trailed throughout a scrappy contest that saw the visitors prevail on Friday.
A quartet of Ihaia West penalties in the first half had La Rochelle in the clear, with only Maxime Machenaud's three-pointer on the stroke of the interval getting Racing on the scoreboard.
Arthur Retiere went over early in the second half for the opening try, which West converted to give La Rochelle a commanding 16-point lead.
It was not as straightforward as the away side might have hoped from there, however, with Leone Nakarawa crossing 13 minutes from time.
But while Teddy Iribaren's conversion, plus a 73rd-minute penalty cut the gap to six, La Rochelle clung on to progress in the play-offs.