Indian Wells, California: Argentina's Juan Martin del Potro upset World No. 3 Andy Murray 6-7 (5/7), 6-3, 6-1 on Friday to reach the semi-finals of the ATP Indian Wells Masters.
Del Potro, the 2009 US Open champion, beat reigning US Open champion Murray for just the second time in seven meetings and booked a clash with World No. 1 Novak Djokovic for a place in the final.
Djokovic earlier remained unbeaten in 2013 with a 6-3, 6-1 victory over France's Jo-Wilfried Tsonga.
The defeat means Murray will have to wait longer for a chance to overtake Roger Federer for the second spot in the world rankings.
Murray could have risen to No. 2 for the second time in his career by reaching the final here after Federer bowed out in the quarter-finals.
But the Scot was never able to break del Potro's serve and was undone by eight double faults of his own -- the last coming on match point to bring things to a close after two hours and 32 minutes.
"It was a tough match," Murray said. "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. That's maybe what happened today."
After the first set went with serve throughout, Murray was quick to take charge of the tiebreaker.
A forehand winner gave him a 5-2 lead with two serves coming up, but he served up a double fault and netted a forehand to let del Potro pull back to 5-4.
A backhand long from the Argentinian gave Murray two set points at 6-4. Murray was off-target with a backhand on the first, but a backhand error on the next from del Potro gave Murray the set.
Murray couldn't build on his advantage, however, dropping his serve at love with a double fault on break point in the second game of the second set.
He steadied, but with del Potro vigorously defending his serve, the break was the only advantage the Argentinian needed to take the set.
Murray mustered his first break points of the match in the third set, but couldn't convert either.
On the first -- in the second game of the set -- Del Potro came up with a big second serve that caught the back of the line.
On the second, the Argentinian's shot was slowed by the net cord, catching Murray off guard.
"He had hit quite a hard shot, so I had planned on running quite hard into that corner," Murray said. "That net cord changed the direction of the ball a little bit and slowed it down. Then I mis-hit it."
Such points can be the difference sometimes, 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."