Wayne Routledge netted a last-minute winner as Swansea beat United 1-0 at Elland Road yesterday.
Leeds had more than enough chances to kill off the game as a contest well before Routledge's late goal.
But despite being the dominant side, Cooper believes that Marcelo Bielsa's side could have gone behind earlier than they did.
Sam Surridge went down under a challenge from Casilla on 81 minutes but referee Darren Bond was not convinced.
Cooper, however, was. He told Swansea's official website: "It's a clear penalty as well that should have put us 1-0 up but then we get the goal from Wayne from a set-piece."
Really, Leeds could and should have put the game to bed even before the incident that Cooper is referring to.
There was a touch of 2018-19 about Bielsa's side yesterday, in the sense that there was plenty of possession and opportunities but very little ruthlessness when it mattered.
And the Argentine, whose side now have a two-week break, will be hoping that it's more a blip than the start of a recurring theme.
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