To make his point, Keown highlighted similar mistakes by Mustafi against Southampton and Newcastle as he allowed a player to score after beating him to a cross in both games.
Kenedy, who had struggled to get himself into the game before the break, belatedly started to make an impression and Benitez sent on loan signing Islam Slimani in place of Gayle as he looked for a victor.
Although the Europa League semi-finalists remain in sixth spot, the gap with seventh placed Burnley is now just two points. Mustafi had a great start to life as an Arsenal player, initially rejuvenating the back four and forming a good partnership with Laurent Koscielny.
Arsene Wenger has revolutionised their club but Arsenal fans have rejected it for some time now, even though the entertaining football has continued to flow.
'There are people that talk about "Young coaches and we give them time", but when a club wants to win quickly what they want is results and results with people who have been here for a while and know what the Premier League is and how hard it can be'.
But it was Newcastle who landed the knockout blow in the 68th minute.
"Now we want to keep going and try to finish as high as we can in the table", he added.
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The 20 top-flight teams voted against introducing the system for the league's 2018-19 season after trial runs in the cup competitions received mixed reviews.
Arsenal supporters just want to count the trophies and they would take Sam Allardyce, never mind Rafa Benitez, if it meant winning the Premier League. "Wenger knows it's not good enough".
"I think (City were) far better over a consistent time", Merson told talkSPORT.
"When you commit so many team mistakes, away or home, you get punished and Sunday proved that".
They were too strong for Arsenal on Sunday and have been at the heart of the team's run of four consecutive league wins.
Iwobi toe-poked a 21st-minute effort straight at Dubravka with the home side riding their luck, although had Shkodran Mustafi not got in a vital touch as Dwight Gayle controlled Jonjo Shelvey's ball over the top seven minutes later, they might have been back on level terms.