Unai Emery insists Arsenal only have a "50-50" chance of reaching the Europa League showpiece, despite building a 3-1 semi-final lead against Valencia.
Alexandre Lacazette's first-half double and a late strike from Pierre-Emerick Aubameyang put the Gunners in control of the tie going into next week's second leg.
Emery's side recovered from an extremely shaky start which saw Mouctar Diakhaby head an 11th-minute away goal for the Spanish side, after Valencia defender Ezequiel Garay earlier missed an open net.
"It's a good result at home in the first leg but the second leg is going to be very difficult and maybe different," said Arsenal boss Emery, who managed Valencia from 2008 to 2012.
"I consider it to be a 50/50 for the two teams.
"We can be happy today and proud of the players because after 1-0 it's not easy to be calm and come back with this team.
"It's not normal Valencia concede three goals. They are a very, very good team.
"And it is the reason I am very proud of our work today but it's going to be very difficult.
"I still believe that the tie is in the balance, we know how tough it will be to beat Valencia again. And they will be looking to respond."