Leinster are protecting a proud achievement in European Cup finals, having never lost in the showpiece game.
With the chance to equal Toulouse's record-haul of four European Champions Cup wins, Leinster travel to Bilbao this weekend to take on France's Racing 92 in the Irish province's first final appearance since 2012.
Sexton said: "We couldn't get going and they came out and slowed us down at the ruck, which is obviously the way to beat us".
With sevens convert Virimi Vakatawa at outside centre, Racing pose a significant threat out wide and Leinster senior coach Stuart Lancaster is wary of their individual ability.
"It's one of the great challenges that we face as a club moving forward - you see some of the French teams and the resources they have available and the calibre of players they have been signing over the years makes it a great challenge for us". The Top 14 side have another opportunity after progess this year despite finishing second in their pool.More news: Russia, Germany Speak About Preserving Iranian Nuclear Deal
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Racing delivered a devastating first-half performance in the semi-finals which gave them a 21-point half-time lead in an eventual 27-22 victory over Munster.
But Racing have fought hard to reach the final, and proved their worth with a win over Leinster's closest rivals Munster in the semis. His absence will undoubtedly make their task harder although they still have a squad full of internationals including World Cup victor Dan Carter in his final season at the club. But it is their European form this season, which includes dominant wins over Saracens and Scarlets, which is the biggest factor in their favour.
Where to watch Leinster vs Racing 92?
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.
Racing have also suffered a major blow with the loss of captain and scrum-half Maxime Machenaud, who is ruled out of the game in Bilbao with a knee injury, replaced by Teddy Iribaren.