VALENCIA, Spain -- Unai Emery's first campaign will be deemed a success or a failure based upon the 58th and final game of Arsenal's season.

After the dreadful performance in a 1-1 draw at Brighton on Sunday effectively confirmed that Arsenal would miss out on Champions League qualification through the conventional route, this hugely impressive 4-2 victory away at the Mestalla means they'll travel to Baku, Azerbaijan, later this month to face rivals Chelsea to earn a place in Europe's premier competition for 2019-20.

It was Emery's prowess in the Europa League that led to his appointment in the first place. His three straight triumphs with Sevilla between 2014 and 2016 made him an ideal candidate for the role, and while Arsenal's recent slump means their league finish is a disappointment, it's worth remembering that Arsenal started the campaign as very much sixth favourites for the top four.

The Europa League always seemed of huge importance to Arsenal this season, and Emery has successfully steered Arsenal through tricky ties against Napoli and Valencia, where Arsenal have taken two-goal first-leg leads away from home and not merely defended them, but added to their margins of victory.

This was a huge test for Emery, against the club with which he spent a four-year spell and made his name as top-level coach. The home supporters' welcome wasn't friendly, with anti-Emery chants as the Arsenal coach arrived, boos when Emery emerged from the tunnel and an electric atmosphere from the outset.

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Initially, this looked like being a long night for Arsenal. Kevin Gameiro's opener arrived in just the 11th minute, then five minutes later, Rodrigo sent a fizzing half-volley narrowly wide of the far post from outside the box. It would have put Valencia ahead in the tie. Arsenal were hanging on.

But then Arsenal burst into life with a goal out of absolutely nothing. There was a clever touch from Alexandre Lacazette to provide the assist, but this was really all about the finish, swept into the net from outside the box, with the outside of Pierre-Emerick Aubameyang's right foot. It was an unusual, elegant finish and contrasted sharply with his late miss against Brighton at the weekend, when he tried to engineer an outside-of-the-boot finish with an elaborate scissor-kick. In some ways, these incidents summarise Aubameyang, a prolific striker who nevertheless sometimes struggles to convert the easiest of chances.

On this day, he was clinical, but it wasn't just the goals that he and his strike partner earned praise from Emery for: "They are very good strikers, but I am proud of them because of how they worked defensively. We needed that today, and the big players can be good as strikers, but [I am happy] when their commitment is like today, defensively."

But this was his best performance in an Arsenal shirt. It was a game that suited him; with Valencia forced to do the running and Arsenal allowed to play on the counterattack, this meant Aubameyang could concentrate on using his speed into the channels. He and Lacazette rotated positions but positioned themselves wide rather than as a central strike duo, with Mesut Ozil prowling behind in a 3-4-1-2.

Aubameyang, as ever, missed chances. His headed effort from a corner was wayward, his left-footed effort after good interplay on the edge of the box was tame. But this always felt like his game. Toward the end of the first half, he sped down the right and cut the ball back for Lacazette, who swept a shot against the outside of the post. It felt like Arsenal might live to regret that.

Lacazette can let his head drop after that type of miss, but Aubameyang always remains bright, lively and energetic, and it was his determination and ambition that created Arsenal's second, with Lacazette the beneficiary. Aubameyang hesitated when confronted with Jose Gaya, knowing the full-back could match him for pace. And sure enough, his knock past the left-back was reached first by Gaya, but Aubameyang won back possession immediately, the ball fell to Torreira and he transferred it into Lacazette, who made no mistake. Aubameyang had successfully counterpressed his own concession of possession. Valencia now needed four goals, and a once-raucous Mestalla started to empty.

The Gabon international wasn't finished, though. His second came from a classic near-post run across the opposition centre-backs to convert a low ball from Ainsley Maitland-Niles. The 21-year-old had spent the first half under pressure as Valencia concentrated their attacks down his flank but ended the game having provided the most memorable moment of his Arsenal career to date.

And Aubameyang can say the same, after he completed his hat trick with two minutes remaining, slamming the ball into the top of the net from a tight angle on the right. It felt like confirmation of his brilliance, the type of moment Thierry Henry used to provide away from home on European nights in that same No. 14 shirt -- away at Inter, away at Roma and away at Real Madrid, to mention a few.

Those were all Champions League nights, and no Europa League game can ever be considered on the same level. But that, of course, is the whole point: Arsenal desperately yearn for a return to that competition, and on this occasion, Aubameyang looked like a Champions League player in a Europa League tie. Another performance like that in Baku and Arsenal will be back in the big time.