I have seen it, Howson was stood right next to him mate, just outside the penalty area. I don't remember Howson scrambling around for any reason at all, he was stood virtually still, watching the ball. So essentially, Howson lost two players, ended up marking nobody, and then watched the ball roll through the area and still didn't react. But Spence is the one getting ripped to shreds because he is a favourite target of some people.
I thought that Roberts made a difference when he came on and may get a chance if Tav is out. After the goal collectively the entire team gave up (Leadership?). Tav was involved in plenty of moves but invariably he took too long on the ball, too may touches and didn't deliver anything in to Britt (who had reverted to poor).
Warnock did say on a previous interview that it could be 3 players in, but didn't state what position, and said I'd leave it to you (the press) to speculate.
I was thinking through the game and before fry got injured that we don't have a lot of depth in defensive cover especially on the right side of defence. I didn't rate Spence as a right back before the game and still don't now.