By Mark Lamport-Stokes
The big-serving American, who had not won a single set in four previous meetings with Murray, produced his best tennis of the week to wrap up victory in two hours 22 minutes at the LA Tennis Center.
The 22-year-old punched his right fist into the air in delight after becoming the first player to win back-to-back LA Open crowns since fellow American Andre Agassi in 2002.
"This feels great," a beaming Querrey told reporters after winning his fourth successive three-set match of the week. "You're never out of it. You can't give up.
"Today on the break point in the second set and the match point I was just consistent. I wasn't going to give it to him. I was going to make him come up with a shot to beat me."
The 6-foot-6 Californian, ranked 20th in the world, was overjoyed after avenging his loss to Murray in the fourth round at Wimbledon four weeks earlier.
"That's the highest-ranked guy I've ever beat," Querrey said. "The last two sets today were great. I hit some great forehands, I served well when I needed. That was some of the best tennis I've played."
"Obviously I'm disappointed to lose but you've got to take the circumstances into consideration," said the 23-year-old Scot, a late addition to the draw after the withdrawal last week of world number two Novak Djokovic.
"I've got to be happy with getting to the final and having chances to win. I didn't play my best tennis but hopefully that's going to come."
Querrey broke Murray in the third game of the match but failed to hold serve in the eighth and 12th to lose the opening set. The American smashed his racket in frustration after double-faulting on set point.
Urged on by his bare-chested 'Sam-urai' supporters, Querrey failed to convert two break point chances in the fifth game of the second set and Murray followed suit with one missed chance in the eighth.
In the 10th, Querrey faced a match point on serve at 30-40 after pushing a forehand wide but he escaped when the Scot missed an attempted backhand winner down the line before going on to hold.
The set went into a tiebreak which the American, roared on by his fans, dominated to clinch 7-2. He punched his right fist into the air in celebration after leveling the match with a forehand winner down the line.
The final set went with serve until Murray was broken in the sixth game, dumping a backhand drop shot into the net to trail 2-4 before getting blood on his knuckles after pounding his racket in fury.
Serving for the match at 5-3, Querrey faced a break point at 30-40 but he saved that with a forehand winner before holding for victory.
(Editing by Ian Ransom)