Winning as underdogs requires ample precision and a whole lot of luck. Leinster brought none of the former and were abandoned by the latter in a first half defined by errors, both unforced and otherwise. Those errors cost Leinster the game. In a way, the tone was set inside the opening minute, Hugo Keenan inexplicably spilling the first clearing kick of the day from Maxime Lucu. Cue bedlam in a San Mames stadium dominated by a fervent Union Bordeaux Bègles faithful.[ Live Leinster v Bordeaux: Bielle-Biarrey on fire as French side retain titleOpens in new window ]A crowd doesn’t create momentum on its own, but it sure can help. Every Leinster error was greeted by a cacophony to rival any atmosphere this competition has seen. Keenan’s mistake wasn’t terminal, but James Ryan’s spill 10 minutes later came close. After a long, painstaking set of phases where Leinster’s accuracy held just long enough for Tommy O’Brien to open the scoring, the resulting kick-off went through Ryan’s hands. The ball did rebound off a pink and blue jersey into touch but Bordeaux pinched the lineout. Leinster would not get the ball back outside of their own half for another 15 minutes. They were down two scores by the time they did. 2026 Investec Champions Cup Final, San Mames Stadium, Bilbao, Spain 23/5/2026