The Gunners entered the power-packed Mestalla stadium with the aggregate lead (3-1).
The Copa del Rey finalists scored the first goal, thereby, putting some early pressure on Unai Emery’s men.
Soon the lead was cancelled by Pierre Emerick Aubameyang.
Then stepped up Lacazette with a sublime goal in the second half to put the hosts out of reach.
Engulfed by a swarm of defenders, the French man was still able to produce a precise finish.
The former Lyon player has now scored 18 goals this season with 9 assists and has earned a reputation for scoring in the big games.
Later, Aubameyang completed his hat-trick to seal off the game 4-2, thus ensuring their place in the Europa League final.
The Gunners endured an eventful season under Emery’s first spell in the Premier League.
Watch more Arsenal FC highlights, click here- Latest Arsenal FC highlights
They are currently fifth in the table. Yet, Europa Glory could still hand them a place in the Champions League as they meet Chelsea in the finals.