Valencia offer fans free entry for second leg
"It is an absolute necessity that there is an extraordinary atmosphere at the Mestalla that helps push the side towards the achievable aim of a place in the final in Bucharest," the 2004 UEFA Cup winners said in a statement on Friday.
Radamel Falcao scored twice as Atletico stormed into a 4-1 lead on Thursday but an added-time goal from Ricardo Costa has left Valencia with hopes they can go through to face either Portugal's Sporting or Athletic Bilbao in the May 9 final.
Valencia fans, who will be reimbursed if they have already purchased a ticket, have whistled their team and under-fire coach Unai Emery after some inconsistent results in recent weeks.
The Europa League has been much-maligned by fans as a poor cousin to the more lucrative and prestigious Champions League.