American Brian Harman leads on -12
England's Tommy Fleetwood bogeys last to finish -11
Justin Thomas breaks US Open record with nine-under-par 63 to reach -11
Fleetwood (-12 after 16), Koepka (-10 after 16)
Koepka to go first on 16. Oof he's flirted with the edge of the hole yet again but it's another stinging putt that slides past.
Fleetwood now for a two-shot lead - ooh, he thought it was in but he's pushed it left and has to tap in for par.
Image source, EPAWoo Kim (-9 after 17)
Si Woo Kim can't quite make it a fourth birdie on the back nine but the South Korean is still right up there with a quietly impressive round today.
Image source, Reuters
Iain Carter
BBC golf correspondent at Erin Hills
Image source, EPAWe can see 15 names on the leaderboard from where we sit. Not one of them is a major champion.
Garcia in 17th is the leading major winner up there.
Koepka (-10 after 15)
Follow that Brooks! Not quite for Koepka but he finds the centre of the green on 16.
Fleetwood (-12 after 15)
Championship leader Fleetwood at the par 3 16th...
He's gone left, flirting with the bunker...just missed and up onto the back of the green.
It's not going to stay there though! Here it rolls, it's good, it's great - birdie chance!
Fleetwood (-12 after 15)
Calmness personified. Fleetwood is striding round Erin Hills like a multiple-major winner.
A testing distance but the Englishman steps up and strokes in his fifth birdie of the day.
He's made two, maybe three errors today and salvaged all of them adeptly.
He's bogey-free for the round and has only dropped two shots all week. Stirring stuff.
Image source, Getty ImagesHarman (-11 after 14) Fowler (-10 after 16)
Image source, Getty ImagesBrian Harman has a big head on his putter and it's just sliding balls into the cup today. That putter head looks like it weighs a tonne. This blow though ensures he milks the par five 14th for what it's worth to take birdie. We have three men tied for the lead.
Rickie Fowler is just one back. In goes his birdie putt on 16 after a fine iron off the tee. The crowd love it. I get the vibe he's their pick of all those contending.
Koepka (-10 after 14)
It was an outside chance, Koepka rolls up short and settles for par.
Image source, ReutersFleetwood (-11 after 14), Koepka (-10 after 14)
Decent chip from Koepka to give himself an outside chance of birdie.
He's been outdone by Fleetwood here though, rescuing the situation from the path with a delicate chip. Could be a birdie on the cards.
Harman (-10 after 13) Fowler (-9 after 15)
Brian Harman and his slow play don't get much joy on 14 as his attempt to run the ball off a few slopes on the green is off point. He ends up with around 15ft left for birdie.
Rickie Fowler has some momentum and attacks the par-three 16th to get a look at birdie.
So who are you guys picking? Justin Thomas? Or will he feel the pressure.
Snedeker (-8 after 17)
Well hello again. Snedeker chips on the last but leaves it short and has the most unwelcome sight of his ball rolling straight back to his feet.
His does better with his fifth shot, but now has a tricky putt to 'salvage' a bogey.
We've been asking if you or a friend has a golfing lookalike. We've had some great entries but this is a real challenger for the crown.
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Koepka (-10 after 14)
"That's horrendous."
Not my assessment, but Koepka's of his tee shot on 15.
He's had an escape too, rolling up just short of a bunker.
Fleetwood (-11 after 14)
Joint-leader Fleetwood with his tee shot on the par four 15th.
It's left. It's very far left. Oh, lucky boy - a wayward shot but it lands right next to a path in amongst the supporters who have flattened down the grass.
Still a tough second though.
Image source, EPAFowler (-9 after 15)
These might be helpful, Rickie.
Rickie Fowler with the bucket and spade out on this short par four. Good dig, lands and runs along nicely. He has 10ft for birdie and that's no problem, middle of the cup.
Casey (-4 after 13) Harman (-10 after 13)
Paul Casey trying to get something from this train wreck of a round. The par-five 14th may serve up an eagle... not today. That second shot is short.
His playing partner Brian Harman is impressing everyone by simply staying in this. Three under for his round, if he makes birdie here he ties the lead. Go on Brian, hit the big dog off the deck and go for the green in two. No laying up son...
He wipes the grip down and is beginning to annoy me with how long this is taking. He's short of the green, well placed.
Fleetwood (-11 after 14)
And Fleetwood follows his partner Koepka to birdie the 14th, a much more straightforward effort and it takes the Englishman to 11 under.
He shares the lead with Justin Thomas, with four holes to play.
Koepka (-10 after 14)
Huge eagle chance for Koepka at 14 for a share of the lead.
He's belted it and it's on line...woowee it clatters the lip and jumps over the hole.
It might have dropped if he hadn't have put everything behind it.
Brave return putt to secure birdie. He moves to 10 under.
Fowler (-8 after 14)
Rickie Fowler over the tee on the 15th. A par four but just 288 yards. He is hunched over, away from his ball with club in hand. Some thinking time. Can he get this close and bring eagle into play like some have today.
He whisks it off the peg but an instant "aahhh" tells you it's not ideal. Indeed it's short and in the bunker.
Image source, Getty Images5 live Sports Extra
Chris Latchem
BBC Radio 5 live commentator at Erin Hills
Si Woo Kim is trundling along really, really well, he's just rolled in a birdie putt on the 15th to be two shots behind the lead.
You can listen to Chris and the team by clicking 'live coverage' at the top of this page.
Image source, Getty Images