Maybe, the worst part for me was that Tadic failed to stop the cross and presumeably Davis should have done a better job marking, or atleast making life harder for Costa considering both CBs were pre-occupied.
Perhaps he could have come off his line yes, but Id say an unchallenged cross and header were worse. That said, he is hesitant to coming off his line, and he needs help with that.
All in all though it was an excellent performance from everyone and pointing blame at anyone is a bit harsh.