Cochran, who clinched his maiden major title in the over-50 ranks at the 2011 Senior Open Championship, fired a five-under-par 66 to end the day at seven-under 135, level with good friend and fellow Kentucky native Kenny Perry, who also returned a 66.
Japan's Kiyoshi Murota was two shots off the pace after carding a 70 in tricky gusting winds, with first-round leaders Jay Haas (72) and Duffy Waldorf (72) a further stroke back at four under along with fellow American Loren Roberts (68).
Cochran, who tied for seventh in the 1992 PGA Championship played at Bellerive, has relished playing alongside Perry over the last two days in the first of the season's five senior majors.
"It's been a great couple of days," the 54-year-old told reporters after soaring to the top of the leaderboard with a mix of seven birdies and two bogeys. "We have always pulled for each other and continue to do so.
"My son caddies for me and one of my best friends caddies for Kenny Perry and he's one of Kenny's best friends, too. So we had a good time out there."
Cochran, who began the second round at the par-four 10th, made his stunning move up the leaderboard with birdies at the 17th, 18th, first, third and fourth.
"In this round I had an opportunity to kind of get in a groove and get in a rhythm," he said. "Yesterday I didn't hit it very good. Today I was right on the money. Felt like I played a pretty good round."
Perry, a 14-times winner on the PGA Tour who has triumphed twice since competing on the over-50 Champions Tour, was equally thrilled to play in Cochran's company.
"It's been pretty neat for me to play alongside him for the last two days and for both of us to play tremendous," the 52-year-old Perry said after a flawless five-birdie display.
"Russ is kind of the guy I always looked up to. I got better because I tried to aspire to be a lot like Russ."
The cut fell at four-over 146 with 80 players advancing to the weekend.
Among those missing out were Mark Calcavecchia, Scott Simpson and Curtis Strange, all former major winners on the PGA Tour.
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