* Murray seals victory in just under three hours
* Britain will meet Italy in quarter-finals (Adds quotes, detail)
Feb 2 (Reuters) - Britain celebrated their first Davis Cup victory over the United States since 1935 when Andy Murray beat Sam Querrey 7-6 6-7 6-1 6-3 on Sunday in the World Group first-round tie in San Diego.
Wimbledon champion Murray broke his big-serving opponent five times on the red clay surface to give Britain an unassailable 3-1 lead and the final match of the rubber, between James Ward and American Donald Young, was scrapped.
Roared on by the minority of British fans in the stands at Petco Park, 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.
Murray yelled out in delight when the match ended as a backhand service return from Querrey sailed wide, giving Britain their first success in a World Group tie since beating Spain 4-1 in 1986.
"It's obviously nice," Murray, 26, said in a courtside interview after winning both his singles matches in San Diego. "You want to try and contribute as much as possible in these weeks.
"James had a great win against Sam on the first day to put us in that position and it was up to me to try and close it out today, and thankfully I managed to do it."
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, Davis Cup champions on nine occasions but not since 1936, will travel to Italy for the quarter-finals and Murray spoke about the prospect of going on to clinch the coveted trophy for a 10th time.
"It's obviously a goal," the Scot said. "This is the first time I have been involved in Davis Cup when we have had a chance of winning the competition.
"It's going to be extremely tough but we have a great team spirit, we have won a lot in the last few years and hopefully we can keep it going."
Murray made an ideal start on Sunday, breaking his opponent's serve in the opening game when the American netted a forehand, but Querrey broke back in the sixth after hitting a two-fisted crosscourt backhand winner.
Though the American failed to hold in the seventh after blasting a forehand wide, he again broke the Scot's serve when trailing 4-5 after unleashing a searing crosscourt forehand service return winner.
The opening set went into a tiebreak and Querrey led 4-2 before Murray clawed his way back to clinch it 7-5, winning the set in just under an hour when the American netted a forehand volley.
Querrey came under pressure in his first service game in the second set but upped a few gears as he came from 30-40 down to hold before winning the tiebreak 7-3 with a crunching forehand winner to level the match.
However, the American was broken in the first and third games of the third, on both occasions after hitting forehands long, and Murray went on to take the set in 30 minutes when Querrey, having saved three set points, netted a forehand.
Murray broke Querrey for a fifth time in the sixth game of the fourth set when a net cord struck by his opponent bounced wide and the American saved a match point in the eighth before holding to trail 3-5.
Serving for the match, the Scot wobbled at 15-40 after making a double fault but he regrouped with his renowned defensive skills before clinching an emotional victory when Querrey hit a backhand service return wide. (Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Ed Osmond)