Incredible. Justin Rose dribbles a 30-footer into the cup...looked way too left then curled in through the side door. That's a share of the lead. Brilliant. Third birdie in four and he's level par.
And Jason Day keeps his bandwagon rolling on. Birdie at the 8th and he's on +1.
Relief for Luke Donald. This boy's had bogeys galore, he's hit a spectator and watched his partner stroll up to the top of the leaderboard. But he's a got birdie on seven. Back to +5.
NEWS ALERT: Justin Rose leads on his own. After five pars, Mahan gets a bogey to slip back to +1.
Martin Laird, who carded a 68 to finish on +11, says: "It's the hardest last five holes I've ever played. It is a very tough golf course. I can maybe understand why some people like to see the golfers struggle, it definitely brings us all back down to earth. If they're aiming to test all assets of your game then they definitely do that. I'm glad it's over."
Bogey on the 14th and then a par for Westwood and the Englishman is on +7.
Poulter calmed down after that triple bogey on five with five pars but the dreaded bogey returned and he's on +10.
Rory ended the day with four pars and a fourth round 76 to quietly finish his week's work on +14.
Jason Day pops in a cutie on the 10th and the Aussie shares the lead with Rose. England v Australia. The Ashes at the Merion is it?
Mickelson's birdie putt thinks about popping into the cup but races on at the 7th.
After two birdies in three holes, joint-leader Jason Day finds the wet stuff at the 11th.
Ernie Els has roared back with a second birdie in three at the 17th to move onto +4. Don't rule this boy out!
Sizzling from Jason Day. Found the drink, almost found it for a second time and then chips straight in. A dropped shot at the 11th but that 5 could easily have been a 7. Big smiles from the bearded Aussie.
It's been a pretty quiet 20 minutes. Day, Mahan and Rose battling at the top while Mickelson fighting desperately to get back on track. Where do you see this one going then? All thoughts please through the comments page.
Oh unlucky for Mickelson. He slaps his putt from 40 feet and it literally flies over the left edge of the hole ...that left arm's got some wellie.
Clubhouse leader Jason Dufner (carded 67 and is on +5): "I was trying to post a good number. I fought back and felt I needed another birdie. These holes are tough. 15 is tough because of the wind. Location of 16 is tricky."
We're into the second half and nine holes to go. Oooofff Justin Rose pulls up short (could have done with some Mickelson power there) and it's a bogey and there are now no players on under or level par. Day and Rose share the lead with the Aussie sinking a semi-tricky par putt.
Oh lordy....listen up everybody. This is incredible. Magic Mickelson. Hole 10 and he chips in from the rough ....and he's jigging and dancing like a schoolboy. If that was me I'd have stripped off and jumped into the lake...amazing. That's an eagle and he's back leading again. Permission to say WOW.
Mickelson struts onto the 11th and he is pumped. Needs to take a breath before teeing on the 12th. Meanwhile, anything you can do I can do almost as well...Justin Rose is close to the pin with a great birdie chance a few minutes after three putting.
I knew things would liven up as soon as I mentioned it was going a little quiet.
And Rose pokes it in to get that lead again alongside Mickelson.
Weather update....thunder rumbles. Rain is falling. And Rose isn't happy. He tees off at the par three 13th and turns to the gallery and says "Bit early" after receiving the "get in the hole" treatment on his downswing. His ball is safe though.
Westwood ends up with a 73 and +9. A mucky old day for Lee that.