Batter-Runner Steps Over First Base

 
With no outs and no runners on base, the batter (B1) grounds deep to the shortstop. The shortstop fields the ball and throws to first base. With the first baseman's foot firmly on the first base bag, the first baseman catches the shortstop's throw --- but the ball is caught just AFTER B1 steps OVER the first base bag (without B1 ever making contact with the bag).
 
The first baseman tagged the bag while he had firm control of the ball BEFORE B1 touched the bag (so, shouldn't B1 be called "out"?) On the other hand, B1 beat the ball to first base (so, shouldn't B1 be called "safe"?) As the field umpire, what do you do?
 
A) Call B1 out since the bag was legally tagged by the defensive before it was legally tagged by B1
B) Call B1 safe since B1 beat the throw to first base
C) Make no call and watch the actions of B1 and actions of the first baseman in order to determine if "safe" or "out" should be called.
 
Call
In the situation below, the batter-runner passed first base BEFORE the ball -- therefore the umpire should call the batter-runner "safe". The batter-runner is subject to a defensive appeal until he returns to first base to properly touch first base. It is a defensive player's responsibility to recognize the missed base and make a proper appeal.