This is not a surprise. Carrasco entered camp as the favorite to win the spot, in a competition that also included not just Tomlin, but Trevor Bauer (also to begin in Columbus) and Aaron Harang (who the Tribe released, and has since been signed by the Braves). I think Tomlin pitched a bit better than Carrasco over the last month, but Carrasco is out of options, while Tomlin is not. Carrasco pitched well enough that it makes sense to give him the spot, under the circumstances.
Carrasco was a disaster in 7 starts in 2013, averaging fewer than 5 innings a game, with an ERA of 9.00 and an OPS-against of 1.005. Basically, every hitter was Mike Trout against Carrasco when he was a starter. He did better as a reliever, and I still tend to think that's where his future lies. The talent is there for him to succeed in the rotation though, and as long as the leash is fairly short, I have no problem with this move. Tomlin will almost certainly be called up at some point, whether it's because Carrasco is struggling, or because someone is injured. He had the best velocity of his career this spring, and I'm curious to see how he might do.
Danny Salazar is reportedly ready, and will start the home opener on Friday, April 4 against Minnesota. Carrasco will then make his first start the next day, in front of a much smaller crowd. Let's hope he does well and gets on a roll.