Alexandre Lacazette insists Arsenal must stop conceding goals from set pieces if they want to book their place in the Europa League final.
The Gunners will take a 3-1 lead to the Mestalla thanks to a brace from the Frenchman and another from Pierre-Emerick Aubameyang in the first leg of their semi-final tie.
But there defensive frailties were once again on show at the Emirates on Thursday.
Ezequiel Garay somehow missed the target from yards out early on in the contest and the Gunners failed to learn their lesson with Mouctar Diakhaby giving the visitors the lead after 11 minutes, capitalising on some slack marking to head home from close range.
Prior to the tie, Arsenal had had conceded nine goals in their last three games and Lacazette admitted post-match they cannot afford to make similar mistakes in next week’s second leg.
"We conceded the first goal from a set-piece,” he told BT Sport. “At this moment we are conceding too many goals to set-pieces so we need to be careful in the second leg.
"But we showed good character."
Arsenal are still not certain of a top four finish in the Premier League with just two games of the season remaining and Lacazette insists finishing the campaign with a trophy remains their biggest target.
"We want to win the Europa League to go straight to the Champions League but also to win a trophy. We want to finish in the top four in the Premier League and if we can go to Baku [for the Europa League final] it will be special."
