Arsenal's performance in the first and second-half during their 3-1 win over FC Cologne in the Europa League on Thursday (14 September) was as stark as night and day and Arsene Wenger believes the introduction of Sead Kolasinac after the interval was the turning point.

A much-changed Gunners line-up looked woeful in the first-half at the Emirates when they failed to create any clear cut chances apart from two headers which were comfortably gathered by the opposition goalkeeper. They went into the break with boos ringing around the stadium and trailing 1-0 following a wonder goal from Jhon Cordoba.

Rob Holding, who had a poor first-half, was replaced by Kolasinac as Wenger decided to ditch his 3-4-2-1 formation and go with a 4-2-3-1 which saw Nacho Monreal move in alongside Per Mertesacker in the centre of defence.

The French coach believes a change in formation gave Alexis Sanchez more freedom to play higher up the pitch as he felt the Chilean was playing too deep in the first-half.

The tactics immediately paid dividends as Kolasinac, who was a constant threat in attack, slotted in Arsenal's first of the night with a thumping volley.

Despite not being 100% match fit, Sanchez was a constant threat and it finally paid off in the 67th minute when the Chilean cut in from the left, beat two players and curled in an unstoppable shot into the top corner to give the Gunners the lead.

Hector Bellerin added a third with nine minutes left to play to wrap up the points, but Wenger reserved special praise for Sanchez who he believes 'came alive' in the second-half.

"I moved to a four [at the back] in the second half and Kolasinac gave us a lot going forward, but as well he pushed Sanchez more forward. Sanchez played very deep in the first half and when he had more support on the flanks from Kolasinac, he became more dangerous," Wenger said of his decision to change formation during the break, as quoted on Arsenal's official site.

"I think in the second half, he became alive. He's still running, fighting to come back to his best physically. But Alexis is Alexis – he's an exceptional player and even if he's not completely back today, physically, he is an exceptional football player and he can deliver a decisive pass or a goal at any moment," the Frenchman said.

Alexis Sanchez
Alexis Sanchez (R) and Sead Kolasinac scored as Arsenal beat FC Cologne 3-1 in the Europa League Getty