But I was under the impression stopping a breakaway cynically was an auto yellow.
If you commit a foul solely for the purposes of disrupting play, then that is unsporting and a yellow. The non-called, second yellow falls into that category.
But for the first yellow, it's not clear to me that Matic's foul was "professional," as opposed to simply a mistimed, possibly-a-little-desperate challenge. He does get the ball. Which I realize does not negate the foul, but it does call into question whether he was cynically just playing the man.
So if you view the first yellow as possibly being a little harsh, then I can see why you might cut the player a bit of a break on the second yellow. Saints had the advantage, but it certainly wasn't anywhere close to DOGSO.
But this is why DOGSO is such a stupid rule. If Matic makes that same tackle 20 yards up the pitch not on a breakaway, it's not a yellow card. But because it happened in the penalty area, it could be a red card, 2 game suspension, and a penalty. And because of that, everyone expects at least some kind of card for any foul in the area and people view the yellow on Matic as lenient because he could have seen red. And then they wonder why players dive.
That play was very similar to the Fonte play against Liverpool. Fonte also got the ball, but once he launched into that tackle there was no way he wasn't also going to take out the player in an unsafe manner. But Fonte got nothing. In part, I think because it wasn't that great of a goal scoring situation. It probably would have resulted just a cross. And a penalty kick would have been rather harsh for a mistake foul. And yet if that play takes place 20 yards up the pitch no one would have had a problem with a foul being called-- not a yellow, but just a foul.