Murray is just two wins away from retaining his title in the men's singles tennis category at the Olympic Games, but faces a tough opponent in Nishikori, who has been equally impressive at the quadrennial sporting event.
However, Johnson began to find his range with a powerful forehand and while strong on his own serve, Murray could find no way through on the Californian's whose early break was enough to wrap up the second set.
The last four showdown will take place on Saturday and Murray will surely need to play much better to make the final.
"Andy gave me a lot of pressure and my concentration just wasn't there to beat him", said the fourth seed.
Learn about three-time Grand Slam victor Andy Murray, reigning Olympic men's singles gold medalist and current world no. 2. "It's obviously not an easy thing to do".
Neither showed any physical weakness in a three-hour contest that was played in a raucous din and which ended with Del Potro flat on the court after a 5-7 6-4 7-6 (7/5) victory. She will compete in the final for what may be her country's first medal of the Rio Games.
But the Briton will have his work cut out for him today.
Del Potro seemed to draw energy from a blue-and-white-clad contingent of fans from Argentina, whose loud chanting from the rafters - typical of Argentine soccer matches - at times drew rebukes from the chair umpire on Saturday.
Del Potro, who knocked out world number one Novak Djokovic in the first round, won the pair's most recent match in Shanghai in 2013. He converted the second on a miss by Nadal, who made only six unforced errors in the first set and 25 over the last two. Nadal now has a chance to add a bronze medal to his gold medal from the 2008 olympics.
The Scot, who repeatedly grabbed the back of his left leg towards the end of the match, is aiming for a prize spot in history as the only man to win consecutive Olympic men's singles titles. Nadal skipped the London Games due to a knee injury. He beat Stan Wawrinka at Wimbledon, stunned Djokovic in the first round here and, after an Olympian effort against Nadal in last night's semi-final, he stands on the verge of winning gold for Argentina, four years after winning bronze in London.
"I didn't expect to reach the final, beating Djokovic and Rafa", del Potro said, "but I did, and I get a medal, and it's fantastic for me".
But the silver means the 36-year-old matched the most medals won by a tennis Olympian, equaling the five held by Britain's Kathleen McKane Godfree from the 1920 and '24 Games. He did not play again after the grass court grand slam until the Rio tournament.
Andy Murray is the first man to win Olympic singles tennis gold on two occasions. Safarova and Strycova had defeated three-time champions Serena and Venus Williams in the first round but were beaten by Russia's Ekaterina Makarova and Elena Vesnina in the semi-final. But Hlavackova was accidentally hit in the eye by Hingis and her challenge fizzled out as a result.
The rest of the money will be placed in a fund for Akalia, which she can't access without court approval until she turns 18. The money is reportedly being put in annuities that will provide her with $10 million over her lifetime.
Dan Tierney, a spokesman for Ohio Attorney General Mike DeWine, said in a statement that the state would appeal the ruling. Wade , yet again, an activist judge is fabricating "rights" out of thin air to the benefit of the abortion industry".
Just for good measure, rookie place-kicker Roberto Aguayo clanked one off the upright on his first kick, a 33-yard point after. Early on, it appeared Wentz may not have recognized a corner blitz, which led to him taking a big hit on an incompletion.
Dujardin earns her third gold medal in Rio, tying cyclist Laura Trott for the most decorated British female in Olympic history. Remarkably, such is the chemistry between horse and rider, Dujardin has never been unseated in all the years of riding him.
Trump's position has been clear from the beginning, he's under audit, when the audit is finished he'll release his returns". Trump spokesman Jason Miller says claims that volunteer poll observers could be a form of voter intimidation are unfounded.
It's true that exchanges attract mostly low-income people who likely have health issues and can only afford the lowest premiums. Critics have also predicted that huge losses will result if insurers exit from Obama's ACA plans on individual exchanges.
At the same time, the USA is significantly rethinking its estimate of the strength of the ISIS presence in Libya. The official said that after the convoy headed north, ISIS fighters broke off from the civilians and dispersed.
A BP gas station, the scene of an earlier confrontation with police this summer, was torched, the Journal-Sentinel reported. The police chief said he wasn't sure what prompted the stop but described Smith's vehicle as "behaving suspiciously".
The measure was less popular on the mainland, where investors have other vehicles for sending money overseas to invest. China's Shanghai Stock Exchange Composite index and the Shenzhen CSI300 index rose to 7-month highs today.
But she Whatsapped me and said "we've got the boobs, we've got the a**, so let's go in there and give them a show to remember". Following the announcement, CHLOE said her goodbyes and left the house, greeted by boos from the crowd and met by Emma.
Tesla's next Model S could have more than 300 miles of range
It has been estimated that the larger battery pack will allow the Tesla Model S to go for about 300miles on a single charge. Jason Hughes posted information online about the existence of the new model, including a picture of the P100D logo.
Trott extends lead in omnium as Brits dominate again
Hammer ultimately beat D'Hoore by seven points, 206 to 199, but the two were dead even with 40 laps to go in the points race. Hammer was with D'Hoore for second going into the points race, the which is final event of the six-discipline omnium.
Google celebrates Pakistan's Independence Day
Pakistanis will commemorate their national heroes and pay homage to the sacrifices of martyrs for their sacrifices. In Lahore, a Change of Guard ceremony was held at Mazar-e-Iqbal earlier in the morning, Radio Pakistan reported.
With rare humility, Trump concedes he could come up short
When given the opportunity to track back his claim in friendly media territory, the Republican nominee doubled the hell down . Clinton released her tax returns on Friday, painting the move as a sign of transparency that her campaign says Trump lacks.