Murray had won his two previous encounters against Del Potro
Andy Murray produced a sensational display as he beat Argentina's Juan Martin del Potro to reach the final of the Sony Ericsson Open in Miami.
The Briton sealed a 6-1 5-7 6-2 victory and will face Novak Djokovic in Sunday's final, after the Serb earlier beat Roger Federer 3-6 6-2 6-3.
An angry Federer smashed his racquet as the match slipped away.
Djokovic's win means that Murray cannot overtake him as the world number three in next week's rankings.
But the Scot will take great confidence from another fine performance as he saw off Del Potro in front of a partisan crowd in Friday's evening session.
The Scot, 21, had won both his previous matches against Del Potro and started magnificently, while his opponent appeared to be suffering from a draining quarter-final win over top seed Rafael Nadal.
The first set was perfect. I can only hope in the future I can play close to that level
Murray had made swift progress into the last four and looked razor sharp, breaking twice as he raced into a 5-0 lead and quickly took the set.
It was as much a lack of concentration from Murray as anything Del Potro did that saw the Briton drop serve early in the second, having led 40-0, but Murray got the break back straight away and looked on course for the win.
But the longer Del Potro, 20, stayed on serve the more his confidence grew, and he levelled the match with a superb game at 6-5 to send the crowd wild.
The momentum appeared to be with the seventh seed going into the decider as he saved an early break point but Murray remained impressively focused and got the break in game five.
With another break point pending at 4-2, Murray had to wait while Del Potro went to his chair for treatment to his leg, but the British number one converted his second chance of the game and served out the match comfortably.
"There were a lot of highs in the game. I think I only played one or two bad games," Murray said afterwards.
"The first set was perfect. I can only hope in the future I can play close to that level.
"In the first set I mixed it up a bit and kept him moving around. I knew he would be tired after the Nadal game so that's what I tried to do."
Second seed Federer was trying to win his first title at the elite Masters 1000 level since Cincinnati in August, 2007, and the Swiss began Friday's first semi-final well in blustery conditions.
With his forehand impressive, Federer broke the Djokovic serve in games four and six, but the warning signs were there as he handed one of the breaks back before steadying himself to serve out.
Just because I smashed the racquet doesn't mean I lose it
From the start of second set, the 13-time Grand Slam winner's form slumped alarmingly. Djokovic broke for 2-0 and Federer missed with a makeable forehand at break point in the following game.
A Djokovic double-fault in game five then returned the break before Federer recovered from 0-40 in the next game, only to drop serve anyway, and the forlorn-looking second seed rounded off the set with successive double-faults.
His number of unforced errors in the second set stood at 17 - but the deciding set was simply a nightmare for the 2005 and 2006 champion.
A routine backhand volley into the tram lines was followed by three more unforced errors as Federer handed Djokovic the advantage in game two of the decider, and a forehand into the net prompted the usually calm Swiss to smash his racquet in frustration.
Djokovic had been far from at his best in the testing conditions, and a couple of double-faults at 4-0 gave Federer a sliver of hope.
But the Serb remained solid enough to serve out the victory and prolong Federer's wait for another Masters title.
"The key was the patience - something I didn't have in the first set," said Djokovic.
"The conditions were quite difficult. It was a nice breeze on a hot day for people in the stands, but for us players it wasn't easy. That's why there were much more unforced errors than winners."
Of his racquet smashing, Federer said: "I didn't lose it. I was just frustrated. Just because I smashed the racquet doesn't mean I lose it. Didn't feel great, it's just a natural thing I did."
He added: "Once one guy gets the upper hand, the other guy is a bit uncertain. It's tough but he struggled big time in the first set.
"I finished worse than him. He played so bad in the first set, I had a great effort by finishing even worse than him.
"You try hard and then it's just not working. Today it is different just because there's so much wind as well. Once you start feeling bad, it's kind of tough to regroup."