(CNN) -- A second consecutive round of 66 fired Paul Casey to the top of the Memorial Tournament leaderboard in Dublin, Ohio, Friday after overnight leader Rory McIlroy fell away.
Casey shot six birdies and an eagle, which more than canceled out bogies on holes nine and 17, to finish the day on 12-under-par.
The Englishman now sits three shots ahead of Masters champion Bubba Watson going into the weekend.
"I had very good control of the irons today," Casey told the PGA Tour website upon reaching the clubhouse.
"The driving was still good again but I was ecstatic with the way I played. There was a couple of mistakes in there. But that's Muirfield Village. It's a tricky golf course and you don't need to do a lot wrong to make a mistake."
McIlroy had led by three strokes after Thursday's stunning 63 but fell way back to tie for 24th position at the end of day thanks to second round 78 that included three bogeys and three double-bogeys.
The 25-year-old Northern Irishman, who picked up the European PGA title at Wentworth last weekend, had complained of a knee problem after his first round but refused to blame injury for his poor showing.
"I felt it a little bit, but didn't really bother me too much," he said.
"Hopefully that's the bad run out of the way and I can play some good golf on the weekend and get myself back in with the shots," he added.
Elsewhere on the course, a 70 for Chris Kirk ensured he kept up the pressure on second-placed Watson, lying one shot back at eight-under-par.
Japan's Hideki Matsuyama, meanwhile, carded a five-under par round of 67 to tie for fourth with Martin Flores of the U.S. on seven-under-par.
World No. 1 Adam Scott, who won the Colonial tournament last weekend, shot a solid second round of 70 to end the day tied for 10th position at five-under-par.