Kaymer on in two at 18 and he nails his monster eagle putt. That's a 66 for eight under and tied for eighth. Stenson can only make par, he's in with a disappointing 71 for eight under and also tied for eighth. Day goes with iron off the tee at 18, finds the fairway. 

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Day's birdie putt just misses at 17, he now needs an eagle at the last, and even that might not be enough. Walker perfect with his second at 17...

Jason Day with his third at 17. He's got 90 yards, pretty decent, birdie chance up the hill. Walker with driver on 17, middles it...

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Walker races his birdie putt four feet by at 16. Day out of some cabbage at 17, that's safe enough, leaving himself a wedge in. Stenson absolutely flushes his second from 243 yards at 18 and it flies over the top of the pin and over the back of the green. Walker with that par putt, never in doubt...

Walker on tee at the par-three 16th, five iron, tugged it left. Day with driver at 17, fore right, hits someone on the shoulder, but we think he's OK. Streb at 16, right into the guts of the green. 

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Stenson still playing some good golf, here he is with a lovely pitch into the 17th. Koepka in with a 70 for nine under, currently tied for fourth. Day at 16, that's a complete misread, no birdie there, taps in for par and to remain -11, two back. Stenson misses his short birdie attempt at 17, he looks shot.

Day pulls his tee shot left at 16, he's got another huge birdie putt. Walker taking plenty of time over his birdie putt at 15 and when he finally hits it, it stays just left. 

Kaymer bogeyed 16, is now six under. Day with a magnificent save at 15, he's still in the hunt. Walker has branch issues at 15, looks like he'll be punching it short and hoping it will race on... what a shot, lands it straight in the heart. 

Walker with a 12-footer for birdie at 14... stays just left, stays -13. Streb with a great save at 14, stays four back. Walker on tee at 15, goes with driver, finds a tree, think it's scuttled through... Day with a monster for birdie up ahead... hasn't hit it hard enough, and that grin looks like a grin of resignation. Stenson makes par at 16, stays -8. He looks shattered. Matsuyama finally makes one at 18, in with a 68 for nine under. 

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Stenson jabs his bogey putt left of the hole at 15 and that's his bacon cooked, drops back to -8 and five off the lead. Day finds rough off tee at 15, Walker is sitting very pretty at the moment. Did I mention Daniel Summerhays? In with a 66 for 10 under and the clubhouse lead. Walker all over the flag at 14...

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Nobody has made the charge we expected from the chasing pack, everyone has had chances but nobody has been to take them. Here's Matsuyama missing another short one on 17. Walker makes that save at 13, stays two clear. Stenson's challenge is over, he's making a hash of the 15th - muffed his chip, muffed another one, still has a fair few feet for bogey.

Walker races his birdie putt past the hole at 13, that's not a gimme coming back. Stenson with a wedge into the 15th, flies it through. Spieth misses another short one on 18, finishes with a 68 for six under overall. 

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Day with three wood at 14, safely away. Koepka at 15 and he nails a monster to get to -9. Walker at 13, 134 yards left, that's just OK. Day up on 14, 160 yards left, again, just OK. Matsuyama almost sticks in his approach at 17, should at last make a birdie.

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Alas, Spieth missed that birdie putt at 17 and stays six under. Hasn't quite been on his game this week. Kaymer finally makes one disappear at 13, moves to -7. Stenson, however, just misses. The Swede just can't make it work on the greens today. Day makes a great save at 13, stays two back...

Day's second at 13, nine iron, pushed it right. Streb for birdie on 12 but, unusually, he hits it too hard and it lips out. He stays nine under. Walker with a three-footer for par at 12 and he pours it straight in to stay two clear. Spieth with a peach of a chip at 17, he should make that to be -7 and tied for ninth. Stenson sets up another birdie attempt at 14, as Walker pulls out the big stick on 13 and trolleys one down the middle. Day well short with a birdie attempt at 13...

Walker with five iron on the tee at 12... right into the heart. Day at 13, with iron, just makes the short stuff. Summerhays with a long-range birdie attempt at 17, right on line but he hasn't hit it. Kaymer's birdie attempt at 13 looks in all the way but it bends a bit too soon. 

Day with a knee-knocker for par at 12 and that's straight in, he stays two back. Stenson with a birdie attempt at 13 and yet again he hasn't hit it, he just hasn't got to grips with these slow greens. Matsuyama with another birdie attempt and yet again he's missed by a whisker...

Jay Townsend
BBC Radio 5 live at Baltusrol

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Now that was huge putt, an unlikely putt to go in and stretches his lead.

You are getting to the point where things are starting to go in Walker's control, that is when there is more pressure on him.

Stenson and Kaymer give themselves makeable birdie chances at 13. Walker with another long, 30-foot birdie attempt at 11... nailed it, that's two in a row, this could be Walker's day...

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Day stalks his ball on the tee at the par-three 12th, but comes up well short, club out. Stenson flays one down the middle with his three wood at 13, Spieth has picked up a shot at 15 to get into that huddle on -6.