Joint first round leader Greg Norman is well enough placed at 8 under par and just three behind Jackson.
Jackson, from Germantown in Tennessee, is surprised at his effort to date.
"You know, realistically, I was shooting to make the cut, you don't expect to come into this tournament with these guys and say, you know, I want to go win the tournament. I've got guys at home saying, if you played your game you can win."
"I'm thinking yeah right. Yeah, I can beat Greg Norman. But, you know, tomorrow I know I'm going to be nervous. I know there will be rough patches. It's been all popsicles and lollipops so far. But I expect there to be some tough spots. Hopefully we can keep a level head and work through them."
Jackson has played many USGA Championships and has twice reached the quarter finals of the US Amateur although clearly against this field he is playing at a different level. His two round total has tied the previous 36 hole record at the US Open.
Pre tournament favourite Bernhard Langer is in 32nd position at even par.
American based Victorian Graham Banister, is, along with Norman, one of only two Australians in the field and made the cut on the number at 3 over.
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