The England Under-20 star scored one try and set up another for the Exiles.
And Booth said: “Alex is playing in place of former All Black Clarke Dermody and is grabbing his chance with both hands. It’s fantastic.”
Peter Hewat, Richard Thorpe and Sailosi Tagicakibau also crossed for the Exiles.
Charlie Hodgson fired the points for Sale, who have slipped off the top of the table.
Sharks boss Philippe Saint-Andre said: “We made too many errors.”