Arsenal, Europa League semi-finalists previous year, had lost three consecutive Premier League games to drop to fifth place in the table with two games left - undermining their hopes of qualifying for the Champions League via a top-four finish.
At 2-1 and with the clock showing 90 minutes the semi-final was precariously-balanced for the return at the Mestalla next week but Aubameyang's late volley means Arsenal will head to Spain as favourites to reach the final in Baku.
And the Spaniard, a three-time victor of the competition with Sevilla, will take a two-goal lead back to former club Valencia for next week's second leg after Aubameyang struck late on.
Arsenal had lost three Premier League games in a row since winning 1-0 away to Napoli in the last round, but they showed strong character to bounce back after a sloppy start to the first leg. Unfortunately it's out of my hands but I wanted to say thank you to the fans for your support. "I've got two more years on my contract".
De nouveaux heurts à Caracas après l'échec du soulèvement militaire — Venezuela
La veille, des affrontements avaient déjà fait au moins un mort et des dizaines de blessés, selon le gouvernement et l'opposition. Des affrontements ont eu lieu à Caracas , mais Maduro reste au pouvoir à l'approche de la tombée de la nuit de mardi à mercredi.
The impressive victory followed a run of three consecutive defeats in the Premier League, and Arsenal were forced to come from behind after conceding an early goal to Valencia's Mouctar Diakhaby.
Once again, it was up to the dynamic duo up front to restore order, with Lacazette doing what he apparently always does in Europa League semi finals - only Radamel Falcao, with seven, has more goals in such games than Laca (five) since 2010 - in finding the net, before his comic book-loving pal sealed the deal with minutes to go.
Valencia, themselves struggling to secure a top-four spot in La Liga, sliced through the home defence at will and had gone close to scoring before Frenchman Diakhaby put them ahead.
However, the hosts did not learn their lesson and from another set-piece, Valencia took the lead when Diakhaby got the final touch at the back post to force home Rodrigo´s header across goal.
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Granit Xhaka's cross found Lacazette and although his header lacked power it bounced off the turf and just went over the line despite Neto's desperate attempt to keep it out.
Lacazette started the move, releasing Aubameyang with a superb pass.
He made poor contact with a header from an Aubameyang cross before failing to beat Neto from five yards out soon after.
Aubameyang then grabbed what could be a crucial goal at the death when he volleyed in Sead Kolasinac's cross.
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Earlier Thursday, Moore had told Bloomberg TV that he was " all in " and that he expected to be nominated within three weeks. Moore said in a radio interview on April 1 that he and his ex-wife are on good terms now.