The Magic Number is 2

So here we are. 

On Wednesday night both the Rangers (86-72) and Astros (84-75) were victorious, while the Angels (83-74) dropped a game they badly needed, so the West shakes down like this:

Texas can eliminate the Angels from West contention by winning 1 of the season's final 4 matchups between the two clubs. However, if the Rangers manage only one win, the Astros can still tie Texas in the West by winning out. After an off day tomorrow, Houston travels to Arizona to close out its season. 

To make matters simpler, if the Rangers win two games in the LAA series it doesn't matter what Houston does. Texas cannot clinch the West until Friday at the earliest, but it is surely in the driver's seat with four games left in the season.