Tommy Fleetwood said he did not change much leading into day two of the U.S. Open as he shot six birdies to surge up the leaderboard at Shinnecock Hills.

The Englishman, 27, carded a four-under 66 to move into a tie for fourth, but still remains five shots behind leader Dustin Johnson.

It was a remarkable turn of form for Fleetwood, who may have been more concerned about missing the cut after his opening 75, but the world number 12 said he knew things could change quickly.

"Yesterday I was six over through 15 holes and struggling. I missed a few putts and I was on a bad run of bogeys," he said.

"I had three holes left [yesterday], managed to grab one in the last three, then shoot 66 today and all of a sudden you're pretty much in contention.

"It can switch like that, and I think you just have to keep that in mind that you never know what's going to happen, especially in a U.S. Open.

"You don't know what's going to turn. You don't know what the weather is going to do and how difficult it's going to get, but so long as you keep going and hang in there, something may happen or it may not."

Fleetwood has been one of many players to struggle in trying conditions so far, but still believes he has played good golf throughout the tournament.

"I did play well yesterday in tough conditions. I got on a run on the back nine where I had a bunch of five and six foot putts where the greens were not their best," he said.

"I happened to miss a few putts coming in, but there wasn't loads different.  Today I felt like I played really solid.

"At one point, it was the middle of the round and it was [about] just keeping going and trying to survive whilst the rain is there and wind has picked up.

"Luckily, I caught a few birdies at the end, and 66 was very, very good."