Leinster, though, found some reserves of energy and got their reward for a period of possession on the opposition 22 as Racing were penalised at the breakdown.
Racing 92 may be the underdogs going into Saturday's European Champions Cup final against Leinster, but don't write them off.
Leinster have never lost a European final and they managed to maintain that proud record with Nacewa's late contribution ensuring that they ended their Champions Cup campaign unbeaten. Their form in the group stage was impossible to fault as they won all six games which included home and away victories over Premiership champions Exeter and Pro14 Conference table-toppers Glasgow.
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"The way Lambie played against Munster in the semi-finals and the way he has played all season meant we thought he'd be likely to start". The Top 14 side have another opportunity after progess this year despite finishing second in their pool.
This resulted in Racing travelling to French rivals Clermont in their last-eight tie but the visitors produced a dominant second-half performance to overturn a slight deficit and win 28-17.
Borussia Monchengladbach Fans Trolled Hamburg With Clock Banner Counting Down Their Relegation
The end of the game was delayed as Hamburg fans set off flares causing a ten-minute delay. Titz reinvigorated the side over his eight games in charge.
Then, first-choice out-half Pat Lambie went down with a knee injury inside three minutes of the game against Leinster, hit in an innocuous tackle by Rob Kearney and Johnny Sexton.
Teddy Iribaren, deputising for the injured Maxime Machenaud, had kept Racing's noses in front for much of the match and ended with 12 points. This is a significant blow for the outsiders with their influential captain missing.
"If you're working really hard, testing yourself mentally and physically non-stop at a really high pace, when it comes to the game you are more conditioned to it and you feel like you have a little bit more time".
Racing 92 - runners-up two seasons ago - are looking to claim their first title in the club's history.
Sexton and Iribaren traded penalties but also both traded misses from the half way line, Sexton twice.
Sexton levelled in the 16th minute following his own loop with Scott Fardy and a penetrating run from Nacewa, but Iribaren, who impressed along with Camille Chat in a composed first quarter from Racing, punished a maul infringement for 6-3.