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First sign of nerves from Jimmy Walker? He has tugged his drive miles left on the par-five 17th. So far left it's ended up on the blue carpeted area of the courtesy car enclosure.

His caddie is allowed up the steps to retrieve the ball, and gets loud pantomime boos for not making his player hit from where the ball landed.

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Jason Day is only dealing in birdies, five in six for the Australian.

He is making a real challenge now.

Rory McIlroy fails to save par, another dropped shot and at the moment he won't make the weekend. Just a par for Mickelson.

Could be birdie time again for Phil Mickelson on the 13th. His second shot leaves him with a seven footer.

Rory McIlroy plays out of a fairway bunker but his shot ends up in the rough at the back of the green.

Jason Day was also in a bunker but leaves himself a 10ft putt for birdie.

Walker has tugged his tee shot left at 16. I'm told that should he finish 10 under today, he would equal the record for the lowest 36-hole total in a major. Jordan Spieth carded 64-66 in the first two rounds of the 2015 Masters, although his 130 total made him 14 under par (Baltusrol is a par 70).

Grillo with a good save at six, stays two off the lead on eight under. Shot gone for Koepka at 13, despite a neat bunker escape, he falls back to -4. Bourdy of France bogeys one, gets it back on two, is two under par.

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Jason Day is on fire.

He now has four birdies in five holes after more red on the 12th.

Mickelson and McIlroy get par.

Interesting Mickelson is referred to by his nickname 'Lefty' on the scoreboard following the group.

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Grillo punches his second at six just short of the green. Hardly a breath of wind at Baltusrol, Old Glory hanging limp outside the clubhouse. Westwood of England has bogeyed 12 and is -1, compatriot Sullivan has made four bogeys between six and 11 and is also -1.

Jason Day, Rory Mclroy and Phil Mickelson all tee off on the par three 12th.

Mickelson lands on the far left of the green, that will be a long putt for birdie. McIlroy takes a seven iron which leaves him with a 17ft attempt.

Defending champion Day has the pick of the shots, just a nine footer for birdie.

Grillo on tee at six and he's leaked it out right into the wispy stuff. Streb for birdie at the second, he's now six under and four off leader Walker. 

Grillo races his birdie putt by at five and he's got a knee-knocker coming back, and on 14 Walker has made it three birdies in a row to open up a two-shot lead. Grillo makes his par coming back...

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Birdie for Phil Mickelson on the 11th, he has brought it back to one over.

Same result for Rory McIlroy while Jason Day gets par.

Grillo's approach at five and he's stiffed it to within eight feet, Walker's approach at 14 and he's done pretty much the same. Matsuyama at 16 and he leaves his birdie just left, stays -3. Ross Fisher at 18 and he drains a longun for a birdie and to get back to -3.

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Rory McIlroy close to an eagle on the 11th.

His second shot checks on the green and rolls back just past the hole. You would confidently say he should make birdie here, just 12 inches left.

Three birdies in a row for Jason Day as he putts from 17ft. The Australian is on the move.

Lovely chip shot from Phil Mickelson from the edge of the green to within two feet and he leaves with par. 

Rory McIlroy for birdie from 28ft but it's wide and he also takes par.

Johnny Vegas gets to three under courtesy of three straight birdies between seven and nine. WALKER WITH A MONSTER! Back to back birdies on 12 and 13, he's now the outright leader on nine under par, one clear of Emiliano Grillo.

Grillo putting from long range at the fourth... comes up short but should make par to stay eight under. Sullivan for par at nine but he left himself too much to do, drops to -2. 

Phil Mickelson's eight-iron out of the rough lands on the green but skips through into more deep stuff over the back.

I wonder if that fan who was hit got a glove from Lefty?

Brooks Koepka gets to within four of the lead with another birdie at 10, Robert Streb misses with his birdie attempt at the first, his 10th, and stays -5. Walker has birdied a monster on 12 and is joint leader with Grillo.

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Phil Mickelson carded a respectable 35 on the front nine after that opening triple bogey.

But his back nine starts badly as his drive appears to hit a spectator in the crowd. Oddly the crowd seem delighted about that.