The American left-hander completed a level-par 70 on a dry morning at Bethpage for a one-under total of 139, delighted to have benefited from the favourable half of the draw.
Mickelson, who had seven holes remaining when he resumed the second round yesterday, had negotiated a marathon 29 holes the previous day in the best weather of the week.
“We had a great end of the draw and the weather this morning was great,” Mickelson said after offsetting a bogey at the par-five 13th with a birdie at the par-three 17th to trail compatriot Ricky Barnes by seven shots.
“I can’t believe the storm’s coming in. Hopefully it will stay away but the conditions right now couldn’t be better.
“I like the position I’m in,” the world number two added. “I struggled with the putter for the first round and a half and then I started to turn it around there in the end.
“I made some putts and I feel good with it. If I can get hot with the putter, I like my chances in the next two rounds.”
Roared on by huge galleries at Bethpage where he is playing his first major since his wife Amy was diagnosed with breast cancer last month, Mickelson was satisfied with his form from tee to green.
“I’ve been hitting the ball well and my mid-irons have been close, giving me a lot of birdie opportunities,” he said.
“This is a very difficult golf course. It’s long and the rough is very difficult. Just a few yards off the fairways in spots you can literally lose your ball or get an unplayable lie.”
Mickelson, a three-times major winner who is hunting his first US Open title, said he was unconcerned with the scoring by his rivals on the brutal 7,426-yard Black Course.
“I don’t really look too much in the US Open relative to what other players are doing, because it’s just too easy for guys to make mistakes,” he said.
“Once you start coming back, you just come all the way back. I just know that around par is going to be a good score. This year it very well may be under par.
“But it’s only a birdie here or there that gets me right back in it. So I’m not really worried about other players as much as I am about keeping myself under par.”