Let's get this out of the way first: that was a horrible decision by Per. Horrible. That said, that tackle? Not a red card. There was little to no contact, and Diego Costa didn't just make a meal of it, he pretty much made a whole buffet of it. Again: Per was dumb. That was a poor decision on his part. But it was just as poor of a decision on Clattenburg's.
Okay, moving on. Chelsea scored while Arsenal were still trying to sort out their defense following Per's sending off, and of course it was Diego Costa who scored the goal, because that's how these things work. After the sending off, I, like most people, was readying myself for a slaughter, but that didn't happen. After they gave up the goal, Arsenal settled down and actually started creating some chances; they had a much better game in the second half, but a whole lot of wasteful finishing, sloppy play, and general untidiness did them in.
They had several chances to get something out of this game, and they didn't; I'm glad they didn't concede more, but even down a man I'm angry that they didn't get at least a point today.
So, the table is as it was two hours ago; Arsenal are joint second on points but third on goal difference heading into next Tuesday's match against Southampton. But first, there's the little matter of Burnley in the Cup next weekend.