Koepka goes first on 11 and sees his effort curl away from the hole before he knocks it in for par.

Argh, Fleetwood also misses his birdie chance but slides it five foot away. Tricky par but he composes himself and drains it.

Iain Carter
BBC golf correspondent at Erin Hills

One of the biggest debates of the week has been the size of the course at Erin Hills, Iain weighs in...

There's an extra mile worth of walking from the green to the tees at this golf course here in Wisconsin, which is one of the things I have against it. There are many things I like about this course but I love it at a golf course when you can walk off the green on to the next tee and carry on playing.

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Matsuyama in trouble on the par four 15th and is forced to just chip out of the deep rough with his second shot.

He's still got 95 yards to the hole. A par would be a big save from here.

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Tremendous approach from Fleetwood on 11, giving himself a great birdie chance.

He'll have just under eight feet to go to two shots behind the lead.

Ah, maybe not - Koepka uses Fleetwood's ball as target practice and nails it. He'll have a chance to regain that dropped shot too.

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Paul Casey only paid for a single ticket and not a return. Two rounds of quality, two rounds of struggle. Two over today as he ends his round and that's two under for the tournament.

No good being part of the conversation on Friday night. It's Sunday night that counts.

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Matsuyama spins a terrific little chip on 14 right near the hole and drops the simple birdie chance, his third in the last four holes.

He's going to post a very testing clubhouse lead at this rate.

Brooks Koepka has not made a bogey since hole three yesterday. Scrap that, he makes one here on 10, pulling an eight foot putt.

Guy Dixon: Impressed with Harman's stickability. Has what it takes to be a top 10 player.

He's glue-like alright Guy, you're right. Tweet us on #bbcgolf.

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Tommy Fleetwood follows Brooks Koepka in on the 10th, both men have long putts from the back of the green. Brian Harman is on the ninth green and taking 3,670 swings before executing his putt. After all that he does not put any meat on the stroke, perhaps his arms were punched out. Now there is six feet or more for par as he bids to keep the deficit at one.

Harman dribbles it, it's barely rolling but it's in. That's 24 bogey-free holes.

US unless stated.

-14 B Koepka

-13 B Harman

-11 R Fowler

-10 T Fleetwood (Eng), H Matsuyama (Jpn)

-8 B Snedeker, B Haas, C Hoffman, R Henley, J Thomas

-7 T Mullinax, S W Kim (Kor), X Schauffele, B Steele

-6 P Reed

Selected others: -5, JB Holmes, B Wiesberger (Aut), -4, D Lingmerth (Swe), S Garcia (Spa), L Oosthuizen (SA), -3, E Pepperell (Eng), -2, P Casey (Eng), -1, Z Johnson, J Lovemark, M Lieshman (Aus), E, M Laird (Sco), M Fitzpatrick (Eng) +1, J Speith, M Kaymer (Ger), M Fitzpatrick (Eng), +2, A Johnston (Eng), S Lowry (Ire) +7, E Els (SA), L Westwood (Eng)

View the full leaderboard here.

Rickie Fowler handles the 10th well, dinking a bump and run from off the green and sweeping up well with a short par putt. Kim Si-Woo has lost the plot today and makes bogey alongside Fowler.

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Koepka swerves his tee shot on 10 off right and his ball bounces into the rough.

Fleetwood finds dead centre of the fairway.

Brian Harman on the ninth tee, downhill, pin ticked to the back. Sweeps the iron through but she lands short and right. On the green with maybe 40ft to the cup.

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Justin Thomas, a forgotten man in this race. "Hold tight", shouts one fan as the ball leaves the tee. "Down, down, down," says Justin Thomas. It defies him, bunker at the back.

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Who do you guys have picked for this? The back nine on a Sunday can make a mockery of even the best out there. Surely we will not just see a Brooks Koepka procession? Major golf tends to throw up a twist or two on those late holes. Think Danny Willett, think Sergio Garcia. Does anyone have a Garcia eagle in the locker?

Koepka to go first on nine - it's well-paced but just trickles off. Yet another par for the leader. Got to be happy with that.

Here's Tommy...10ft for birdie. Money! Superb bounce-back birdie. He goes to the turn one over for the day but crucially four shots off the lead.

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Rickie Fowler is away up the 10th fairway with power and ping. Brian Harman now has to respond to the Brooks Koepka move. He has around 30ft for birdie on eight. Never going in. Par all day.

Iain Carter
BBC golf correspondent at Erin Hills

Given the wind is due to drop a fraction, I think 14 under has to be the target if you're out there. We've got a couple of par fives for the players still to get through.

Iain has been asking you for today's winning score, give us your views on #bbcgolf.

They started level but are now five shots apart.

A few bragging rights for Fleetwood over Koepka at nine though.

The Englishman sees the American deliver a great tee shot, steps up and betters it with a sublime effort, about 10ft from the hole.

Terrific response from Fleetwood - but he needs to convert.

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There's a little chasing pack behind the main contenders and Brandt Snedeker joins them - a birdie on 11 taking him to eight under.

Can any of them kick on? Can anyone stop Koepka in this form?