Roared on by the minority of British fans in the stands, world number six Murray sealed victory over the 49th-ranked Querrey in just under three hours, improving his Davis Cup record to 18-1 in singles and 21-6 overall.
Ward, the world number 175, had given Britain a commanding 2-0 advantage over the Americans on day one with a shock win over Querrey after clawing his way back from two sets to one down and trailing 2-4 in the fourth.
Britain will travel to Italy in the quarter-finals.
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Frank Pingue)
