After a 75-minute scare, Arsenal booked their place in the Europa League semi-finals by coming from behind to earn 2-2 draw, and thus an ultimately comfortable 6-3 aggregate win, over CSKA Moscow in Russia on Thursday night.

Arsène Wenger's side had for a while looked in danger of joining Barcelona, among others, as victims of an unlikely European comeback, falling 2-0 behind against their hosts.

But goals from Danny Welbeck and Aaron Ramsey, both superbly assisted by Mohamed Elneny, assured Arsenal's progress to the last four.

Here are the five things we learned.

Welbeck the Europa saviour

Those in red and white, along with anyone else of an Arsenal persuasion, breathed a sigh of relief on 75 minutes thanks to Welbeck's emphatic finish, giving the Gunners the breathing space they craved.

The pressure had been on, with CSKA pushing hard for a goal that would have levelled the tie on aggregate and given them an away goals advantage. And it was the former Manchester United forward, cutting in from his station in the left flank, who stepped up for his side.

Linking brilliantly with Elneny, Welbeck burst behind the Russian champions' backline and fired confidently beyond Igor Akinfeev.

That took the 27-year-old's tally for the season to eight, with three goals in his last three Europa League outings. With the World Cup on the horizon, the continent's secondary competition could act as the perfect stage for Welbeck to prove his worth to England manager Gareth Southgate.

Arsenal need Čech upgrade

Both CSKA goals came directly from Petr Čech parrying efforts right back into the danger zone, with the home side's second, tapped in by Kirill Nababkin in the 50th minute, the most glaring of the former Chelsea keeper's bluffs.

Čech failed to properly gather a long-range effort from Aleksandr Golovin, the Russian's standout performer, palming the ball invitingly into Nababkin's path.

The 34-year-old former Chelsea No.1 will go down as one of the best ever between the sticks in the Premier League, but he has regressed to the point where the Gunners now need an upgrade. Wenger must identify a replacement this summer.

Gunners miss Aubameyang central threat

For 75 minutes, Arsenal were desperately blunt in attack. While CSKA were composed, structured and aggressive, they still left holes for their visitors to break into.

Several times Wenger's men worked the ball forward and speed and sought to attack through the centre of their opponents' defence, yet they evidently missed the pace, intelligent movement and clinical finishing of Pierre-Emerick Aubameyang.

The Gabonese striker is cup-tied for the Europa League, offering £52million summer signing Alexandre Lacazaette the chance to show Wenger he didn't need to sign another forward in January. But the Frenchman once again disappointed, failing to hit the target with his two efforts, before being substituted late on.

Golovin Premier League ready

Despite crashing out of the competition, CSKA impressed with their resolve and determination, taking a 2-0 lead on the night, threatening to add to the remarkable comebacks trending around European football this week.

And no CSKA player shone brighter than Golovin, the Russian side's scheming midfield playmaker attracting interest from several major clubs across the continent.

The gifted 21-year-old, who will carry the hopes of the home nation at the World Cup in Russia later this year, stood out with his poise and inventiveness, twice hitting the target, completing two key passes, two dribbles and maintaining an 87.1 per cent pass accuracy.

Despite his tender years, Golovin looks ready to star at Premier League level. Having experienced his talents first-hand, Arsenal should consider a move.

Wilshere's time up

With his contract expiring at the end of the season, it is looking increasingly that Jack Wilshere, once one of Arsenal's proudest and most-promising academy graduates, will be playing his football away from the Emirates next term.

And, put simply, that's how it should be; he's no longer good enough for the Gunners.

Against CSKA, the England midfielder completed a respectable 89.5 per cent of his passes, yet, of all the starting outfield players, only Lacazette (33) saw fewer touches than the 25-year-old (52), who was withdrawn after 68 minutes, with the game still in the balance.

Incessant injuries have taken a toll on his mobility, and he appears to lack the confidence that once streamed forth from his performances. Parting ways this summer is the best solution for both Arsenal and Wilshere.

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