Pro Football Focus did a study on how quarterbacks rate when blitzed. It was an interesting study. They found that Mark Sanchez's completion percentage dropped a bit to 51.95% when blitzed. That was one of the worst in the league. His passer rating was a pedestrian 51.9. However, he matched Peyton Manning's 4.3 touchdown to interception ratio for best in the NFL.
I think there are a couple of different ways to explain it. The first is that these results do not differ too much from Sanchez as a player. Mark is largely a boom or bust kind of quarterback. He has not developed consistency, but he can be exceptional when he is on. He is at least today more of a big play quarterback than a guy who can hit passes with pinpoint precision.
I can also see why he makes big plays against the blitz. The Jets have excellent protection, making them more likely to pick up extra rushers. Mark is pretty mobile and good at extending plays when pressured. He also had some big play receivers in 2010. When a team blitzes, it leaves a lot of one on ones, and the playmakers the Jets had catching passes were apt to win those.
The fact that only 3 of Mark's interceptions came against a blitz indicates what anybody can see by watching, a lot of his errors are self-inflicted, not forced by the defense.