Winter brandished four yellow cards in the first eight minutes and was criticised by both managers.
But Keane said: "It is easy to criticise when you are watching but there were a lot of late tackles going in and overall I thought he did well."
United manager Sir Alex Ferguson was incensed with the way the Gunners reacted to a number of early hefty tackles from his players.
He said: "There were nine or 10 players going round him every time there was a tackle as if it was a massacre. You are looking for the ref to handle the situation, but he didn't."
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