Murray has still to claim a title in 2010 after winning six last year
American Sam Querrey saved a match point on his way to defeating top seed Andy Murray in the final of the Farmers Classic in Los Angeles.
Querrey, the world number 20 and second seed, won 5-7 7-6 (7-2) 6-3 after Murray missed with a backhand at match point in game 10 of the second set.
The 23-year-old Briton had been trying to win his first title of 2010, the last coming in Valencia in November.
Murray had parted company with coach Miles Maclagan earlier in the week.
"If you take the circumstances into consideration I have to be happy with getting to the final," said Murray.
"I had a good week, I enjoyed it. Each match I felt better physically. I played reasonably well, better than the other matches."
Murray had looked on course to put the Maclagan split behind him, despite rarely hitting anything like top form.
The Scot had won all four previous matches against Querrey,
including a fourth-round victory at Wimbledon in June,
and the American appeared overawed in the early stages as numerous errors got him in trouble.
Querrey, 22, let an early break disappear with a poor smash and a wayward forehand in game eight, and three more unforced errors in game 12 handed over the set.
Murray was not at his best but with a first-serve percentage of about 70% he was doing enough to retain control as the second set progressed, although he was fortunate not to drop serve in game five when Querrey made further errors on two break points.
The American was hanging on, with one brilliant lunging volley saving a break point at 3-4, but Murray seemed to be closing in on victory two games later, only to let the opportunity pass by.
Having earned a match point, the world number four would not take the initiative in a long rally and eventually made the error with a backhand into the tramlines.
Murray would not get such a golden chance again, with Querrey racing through the tie-break that followed soon after and then stepping up his game even further in the final set.
It was now Murray who was making the mistakes and in game six a forehand error brought Querrey a break point, which the Briton duly handed over with a tame drop shot that flopped into the net.
He was understandably furious with himself, smashing his racquet in anger, although there was to be one final half-chance for Murray when a nervous Querrey attempted to serve out the match.
But the American saved a break point with another blistering forehand winner and sealed a deserved win in two hours and 22 minutes.
"All four matches were really exciting this week," stated Querrey after his fourth title of 2010.
"It was nice to get through them all and it feels great. This is the first time that I've actually tried to defend a title.
"The last two sets today were great. Andy is one of those players who allows me to hit my shots."
Murray must now regroup before he heads to Canada for the first Masters 1000 tournament of the summer in Toronto from 9 August, with the US Open getting under way three weeks later.
In the doubles final, American brothers Bob and Mike Bryan beat Eric Butorac and Jean-Julien Rojer to set an ATP record with their 62nd career title.
Elsewhere on Sunday, Spain's Nicolas Almagro defeated Richard Gasquet of France 7-5 6-1 to win the Swiss Open in Gstaad, while his compatriot Juan Carlos Ferrero beat Italian Potito Starace 6-4 6-4 to take the Croatia Open title in Umag.