Del Potro, ranked seventh in the world and the seventh seed in this combined ATP and WTA tournament, beat World No. 3 Murray 6-7 (5/7), 6-3, 6-1.[break]
The 2009 US Open champion from Argentina didn´t face a break point until the third set and benefitted from Murray´s eight double faults -- the last coming on match point.
On Saturday, Del Potro will become the latest player to try ending Djokovic´s impressive winning streak, which totals 22 matches dating to October 31 and includes 17 victories this year.
Djokovic dispatched eighth-seeded Jo-Wilfried Tsonga of France 6-3, 6-1.
The departure of Murray, on the heels of defending champion Roger Federer´s quarter-final ouster by Rafael Nadal, leaves only two of the "big four" of men´s tennis in the tournament, which was the first with all four playing since Wimbledon.
Nadal, playing his fourth tournament since a seven month injury layoff, will face sixth-seeded Czech Tomas Berdych in Saturday´s semi-finals while del Potro will tackle Djokovic.
Del Potro beat the Serbian in the bronze medal match at the London Olympics last year, but noted wryly that Djokovic has since beaten him four times -- most recently in the semi-finals at Dubai.
"I need to play better," he said of his chances of beating the dominant player in men´s tennis.
On the bright side, he called his performance against Murray his best match of the tournament.
"I played my game," del Potro said. "I was aggressive all the time, I hit the ball hard all the time with my forehand and I played a few slices as well as drop shots. I think I did a very good game today."
Murray characterized his game as "decent".
He was unable to penetrate del Potro´s serve, never mustering a break point until he had two in the third set.
On the first, del Potro came up with a big second serve, and on the second Murray was caught off guard when his opponent´s shot clipped the net cord and slowed down.
Such points can be all the difference, Murray said.
"I´m not necessarily saying I would have won the match, but you get back on level terms and the momentum is with you," he said.
As for the eight double faults, Murray insisted it wasn´t a major concern.
"There was a lot of long rallies ... sometimes if your legs are just a little bit tired you can miss serves. The timing might go off a little bit and you´re not quite getting up to them."
Djokovic made short work of Tsonga, needing just 54 minutes to get past the lackluster Frenchman.
Djokovic didn´t didn´t drop a point in four service games in the second set against Tsonga.
No sooner had the world´s top player given himself triple match point with a pair of aces then the demoralized Frenchman casually knocked a backhand wide.
"I thought Jo didn´t play his best -- his serve wasn´t going well and that made life easier on court," said Djokovic, who added that he couldn´t concern himself with his opponent´s struggles either mental or physical.
"I really didn´t care about how my opponent felt," he said. "I just tried to focus on the job I need to do, and my performance was really good.
"I served really well and used the shots around the court well, and that´s what matters for me."
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