World number 129 Vasek Pospisil produced the biggest win of his career after upstaging top seed Andy Murray in straight sets at the BNP Paribas Open.

While the gulf in the ATP rankings was evident, there was no gulf in class as 26-year-old Canadian qualifier Pospisil eliminated the world number one 6-4 7-6 (7-5) in the second round on Saturday.

Three-time grand-slam champion Murray - a winner in Dubai last month - was well below his best, especially on serve after recording seven double faults as Pospisil booked his spot in the third round at Indian Wells.

Murray boasted a 4-0 head-to-head record heading into the second-round clash and the Olympic Games gold medallist looked on track to preserve his perfect record against Pospisil early.

Despite a tense opening for Murray, who fended off three break points against a tenacious and fearless Pospisil, the Scottish star took a 3-1 lead.

However, Murray was immediately pegged back as the pair exchanged breaks.

Murray's serve was of particular concern, tallying four double faults and winning just 11 per cent of his second serves, and Pospisil capitalised after firing a forehand winner down the line for a 5-4 lead.

Continuing to work Murray all over the court, Pospisil then claimed the opening set

And he continued where he left off in the second set, full of confidence as a cross-court forehand earned a break point in the first game and he duly converted.

Up a set and 2-0 in the second, Pospisil - whose biggest wins had previously come against Tomas Berdych and Richard Gasquet - was braced for a Murray onslaught and it came when the Briton reeled off three successive games.

It remained fiercely contested as a tie-break loomed and despite saving three match points, Murray was unable to prevent a second-round defeat for the fourth time in his career at Indian Wells.