The £22million January signing was finally handed his first start by Mikel Arteta in the club's Europa League Round of 16 first leg draw in Portugal.
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Arsenal took the lead in the 22nd minute through William Saliba, who nodded the ball in as he got on the end of Fabio Vieira's corner from the right.
But the visitors conceded just 12 minutes later in what was an almost identical goal as Goncalo Inacio headed home from inside the six-yard box from Sporting's set piece.
And ex-West ham striker Dean Ashton didn't hold back in his analysis of Kiwior, insisting he had to be more brave in attacking the ball.
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Speaking on commentary for talkSPORT 2, Ashton said: "It is a carbon copy of the Arsenal goal.
"A brilliant left-footed inswinging corner, Matt Turner, very similar to [Sporting goalkeeper Antonio] Adan, did absolutely nothing, feet rooted to his spot and in drifts Inacio.
"Nobody picking him up, Kiwior ducked underneath it which is embarrassing I have to say.
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"And Inacio just headed it in - guided it in into the far corner - abysmal defending from Arsenal."
Co-commentator Jim Proudfoot added: "Neither Kiwior nor Turner have covered themselves in glory there."
Ashton then stated: "It's just really sloppy defensively, two mistakes, one from the goalkeeper not being brave enough to just come out and deal with that when it's on your six-yard line.
"It wasn't as if he was even under pressure from an attacker that was on top of him.
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"And then with Kiwior, he ducks underneath it with his head going back into his shell, and then we all know that face when you flinch and turn around and something comes at you very quickly.
"And instead of turning and trying to attack the ball, he's flinching away - it's embarrassing."
Arsenal legend Martin Keown was also critical of Kiwior, saying on his punditry for BT Sport: "Kiwior has to do more.
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"Because if I'm playing with this goalkeeper then I'm thinking I'm going to have to head more things."
Ex-England international Rachel Brown-Finnis remarked: "For the Sporting Lisbon goal, Matt Turner hasn't commanded his area at all.
"Jakub Kiwior doesn't help by ducking out of the way, but it would suggest he got a call.
"Turner has to come out and clatter everyone and clear the ball. He hasn't done anything to make his defenders feel confident."
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Arsenal then found themselves behind early in the second half as Paulinho scored on the rebound from close range.
But they hit back almost straight away as Granit Xhaka's speculative cross deflected in off Sporting defender Hidemasa Morita.
Kiwior was then replaced by Gabriel Magalhaes, and despite the Pole's struggles in the first half, Ashton believes he had a decent debut.
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He said: "He's not going to take any glory from the way he defended from the set piece, but plenty of other aspects of his game was excellent."
The scoreline stayed at 2-2, with the tie finely poised going into the second leg at the Emirates next week.