Anderson wins 7-6 (7-5) 6-3 6-7 (2-7) 7-6 (7-0)
Plays Stan Wawrinka in the last eight
Petra Kvitova beats Johanna Konta 7-5 6-3
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Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra
"It might do Andy some good to forget who's in in his box and to focus on the crowd. He's doing a Connors out there."
Image source, Getty ImagesGiven up hope Murray fans? Hold on. Cast your mind back to Wimbledon where Anderson choked against Novak Djokovic after leading by two sets to love up. Although he wasn't two sets and a break up though...
Anyway...back to the present. Murray has a sniff, clawing his way back from 40-15 down - helped by Anderson's fourth double fault of the evening - to set up a break point. That he can't convert but seconds later has another chance....and this time he grabs it!
Piers Newbery
BBC Sport at Flushing Meadows
Murray lets off some steam as Anderson takes a lengthy break off court. Umpire Jake Garner explains it is up to him to judge whether it is a reasonable break. "What's reasonable?" says Murray. "I'm the one who's serving next. I've seen him in there changing his socks."
Anderson finds his groove instantly - and that spells bad news for Murray. Three break points to Anderson and Murray's head is all over the shop. Come on Andy, focus. That he does, saving two of them, but Anderson pulls another brilliant return out of top drawer to nick an early advantage. Murray still isn't happy about Anderson waltzing back onto court at his leisure, chuntering away to the umpire....
Back under way on Armstrong. Unsurprisingly Murray ain't happy, moaning to the umpire about Anderson taking an age to return from the locker room. "I've been waiting for three minutes," he whines. Finally the South African returns and soon gets into his stride...
Philip Studd
BBC Radio 5 live commentator
"Murray has been lacklustre today, he looks like he is running close to empty. You would have expected him to make more of the Anderson serve than he has. There's been no tempo to his game."
Image source, APWhile Murray tries to swear himself back into this game, another Briton will hopefully be much calmer over on Arthur Ashe Stadium. Jo Konta finds herself in the big time. The British number two has reached the last 16 of a Slam for the first time and is about to start against two-time Wimbledon champion Petra Kvitova. Of course, we will be bringing you regular updates right here. Don't go anywhere.
Image source, Getty ImagesTom Gumbleton: Muzz needs a swear jar to be honest...... he gets so annoyed and frustrated way too easily. Worrying.
Andy Murray is furious with himself. He returns to his seat before launching into a flurry of expletives. Luckily it is after the watershed. Then the Briton nips off court for a few moments - presumably to punch a locker or two and calm himself down.
Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra
"Murray is mentally tired. He doesn't seem to have a game plan. He's playing point by point 'lets see what I can do'. Anderson is upsetting him with a clear agenda."
Murray laughs as he squanders a break point - but he is not finding this match very funny, I can tell you that. Anderson shows a few nerves, but finds his composure to set up a fifth set point. Boom...an ace straight down the T does the trick. Or has it? Murray challenges. But the technology tells us that it comfortably hits the line.
David Law
BBC Radio 5 live commentator
"Murray is laughing at himself in the direction of his box. He's pleading with them as if he's saying 'I'm not playing very well, why?' He's shaking with anger because he's not playing the tennis he wants to play."
Despite coming from the other side of the Pond, Andy Murray is a firm favourite at Flushing Meadows. Louis Armstrong shows its support as Murray smashes a forehand winner to move back to 30-15.
An overcooked return hands two set points to Anderson, who sees one disappear down the double fault drain. Another wayward first serve piles on the pressure - and Murray senses a chance. He pounds forward from the baseline, volleying at the net to take the game into deuce....
Paul Christie: Anderson doesn't look like his level dropping. Murray needs to fight fire with fire
Paul: Jo Konta will soon be the last Briton in the US Open. Her best tennis week ever!
AH: Andy's not coming back from this one, won't be making QF this time
Only one person looks less happy than Andy Murray - and that's his missus. Kim Murray looks thoroughly miserable as she tries to bark some words of encouragement to her man. A sizzling Murray serve is too hot for Anderson to handle as the Briton moves 40-15 ahead. A passing forehand down the line lacks the Beckham-like bend to sneak to safety, but Anderson concedes the game with a forehand into the net. The South African is serving for the second set. Again...
Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra
"It just seems like Murray isn't able to get himself sparked up. He needs something special to happen."
Ian in Hampshire: Murray is like the Arsenal of Tennis. Plays some fantastic stuff, wins the title occasionally but your always worried he will lose to anyone.
Sublime stuff from Andy Murray tees up a break point. A backhand drop-volley from Briton gives him some hope of rescuing this set, only for Anderson to force him into a backhand error.
Murray creates two more chances, again failing to convert either. But the third seed does not let the fourth break point slip through his grasp, Anderson slapping a forehand past the baseline.
Glimmer of hope for Murray?
Image source, ReutersNervous start for Anderson as he serves for the second set. A double fault from the big South African gives encouragement to Murray, who is pegged back by some textbook power and placement from the Anderson serve.
A thunderous ace moves Anderson 40-30 ahead, only for another loose forehand to let Murray in through the backdoor. Deuce....
Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra
"It just seems like every time Anderson is under pressure, he comes back with bigger and bigger shots. It's almost like he thinks 'I have nothing to lose, when I'm in trouble I'm going to go for it'. Andy has been tentative."