Pierre-Emerick Aubameyang scored a hat trick as Arsenal beat Valencia 4-2 on Thursday and 7-3 on aggregate in their Europa League semifinal to book a spot in the final against Premier League rivals Chelsea.
Trailing 3-1 from the first leg in London, Arsenal earned a first win on Spanish soil since beating Real Madrid at the Bernabeu in 2006 and kept their hopes of qualifying for next season's Champions League through Europe's secondary competition alive.
"We reacted well to going behind and we knew we had to score a minimum of one goal tonight," Lacazette told BT Sport.
"Auba [Aubameyang] was unbelievable tonight with an incredible hat-trick, so thanks to him.
"We have played badly in the Premier League during the last month and now we have to use this opportunity. We want to play in the Champions League next season and we want the trophy."
Arsenal ratings: Aubameyang a perfect '10' in second leg
The Gunners pulled it even six minutes later when Aubameyang finished off a lovely half-volley from Alexandre Lacazette's pass.
And Lacazette nearly put Arsenal in the lead before the break, but his shot from and Aubameyang cross clipped the outside of the near post and went wide as the teams went to the dressing room tied 1-1.
The sides traded goals before the hour mark when Lacazette picked up a loose ball in the Valencia area and fired home from 10 yards away before Gameiro bundled home from close range after a deflected shot fell to his feet.
The Lacazette strike was a good omen for Arsenal, who are 10-0-0 in all competitions when both he and Aubameyang score this season.
Aubameyang added his second to put the tie away in the 69th minute when he beat his marker to an Ainsley Maitland-Niles cross at the near post to give the visitors the lead and a third away goal.
And the Gabon international finished off a fine team move for his third as full-time approached to complete his hat trick and put Arsenal in the Europa League finals in Baku, Azerbaijan, on May 29.
Unai Emery's team will face Chelsea in the final after their London rivals beat Eintracht Frankfurt on penalties in the other semifinal on Thursday night.