Groggy and shaking
However, after covering the front nine in 37 to fall seven shots off the pace, Day carded five birdies and one bogey to come home in 31 and set the clubhouse target of four under par which was matched by Masters champion Jordan Spieth, Dustin Johnson and South African Branden Grace.

Day, who finished second on his US Open debut in 2011, joint second in 2013 and fourth last year, said: "I didn't feel that great coming out early, I felt pretty groggy on the front nine just from the drugs that I had in my system, then kind of flushed that out on the back nine.

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"But then the vertigo came back a little bit on the 13th tee box, and then I felt nauseous all day. I started shaking on the 16th tee box and then just tried to get it in, really. Last year I didn't play the round after I had vertigo (at the Bridgestone Invitational) and this one was worse. I think the goal was just to go through today and see how it goes."

"I know what it takes to get it done. And tomorrow just need to go out there and focus on one shot at a time. And we'll see what happens," he added. Caddie Col Swatton said Day had almost retired three times but added: "He has played well in the US Open before and is playing well in this one. He just dug deeper than he ever dug before. It was really, really impressive."