I'm intrigued as to why Alexis started at striker now that we have Perez and Giroud, with Welbeck to return.
Trying to think of reasons...
1) Wenger is dead serious about this conversion, and Alexis is going to be our no.1 striker now, with Perez, Giroud and Welbeck all playing second fiddle. If that's the case then I imagine that Giroud and/or Welbeck would be leaving at the end of the season. Not sure on their contractual situations.
2) Wenger really wanted to play with a fast striker this morning, he has deemed Perez not yet ready after the Soton game where he looked very underdone, so he put Sanchez in there. So basically Sanchez would be filling in for Perez/Welbeck until they are 100% fit, before returning to the left flank.
3) Both Giroud AND Perez have been deemed not yet fit enough by Wenger. Perhaps this is the most likely reason?
4) Seems very unlikely, but perhaps Wenger is looking to return to the old 4-4-2, and we need 4 strikers on the books to manage that?