Mitchell is providing McIlroy and everyone else with plenty more fodder through two rounds of The CJ Cup.
One day after matching his career low with a 62, Mitchell followed that with an 8-under 64 on Friday to build a five-shot shot lead going into the weekend at The Summit Club.
Jordan Spieth had eight birdies and an eagle to counter a few soft bogeys for a 65 and was tied for second along with Harry Higgs (67) and Seonghyeon Kim (63), one of eight South Korean players who will be in the second stage of Korn Ferry Tour qualifying next week.
Joining them was Adam Scott, who had two eagles on his final five holes and played his last seven holes in 8 under for a 63.
Mitchell was at 18-under 126, breaking by five shots his best 36-hole score on tour.
"I spent a lot of time in the last few days leading up to this tournament working hard on my game and it's showing," said Mitchell, whose lone victory was in the Honda Classic two years ago. "I'm very thankful for that. Just shows you that hard work pays off as long as you're doing the right things."
Not much has gone wrong for Mitchell.
He was between clubs on No. 10 and had to scramble for par. That indecision carried over to the tee on the par-3 11th, where his worst swing of the day led to his lone bogey. He answered with three birdies the rest of the way to widen his lead.
"If I'm sitting here saying I'm 18 under with only two bad swings, I'm going to take it every time," Mitchell said.
Scores were even lower than the opening round, at least for most players in the 78-man field. That wasn't the case for Robert Streb, who opened with a 61 but was six shots behind when he started his round. Streb ended up 11 shots worse with a 72.
Abraham Ancer made an albatross by holing out from the fairway on the par-5 14th with a shot that rolled onto the green and broke some 30 feet to the left and right into the cup.
Dustin Johnson nearly had one on the par-5 third. His second shot banged into the middle of the pin and settled a few inches away. The world's No. 2 player started with a 74, shot a 66 and actually lost ground. He was 14 shots behind.
Spieth hit a 3-wood so pure that he told his caddie as the ball was in flight that it was a shot he couldn't have hit last year when he was struggling with his game. That led to an eagle on the par-5 sixth, and while he's still five back, he is in range.
"Everybody would have signed for 18 through two rounds," Spieth said. "I think the hardest part is regrouping and almost feeling like you start fresh to put your foot on the gas pedal versus tapping the brakes."
That's the only way to fly around The Summit, which doesn't provide too much stress as long as shots are kept in the grass instead of the desert.
McIlroy brought up Mitchell at the start of the week when the topic turned to how hard it is to win on the PGA Tour. He thought back to the Wells Fargo Championship in May, when he played the final round with Mitchell, trailing by two shots.
"He came out and he hits it in the left bunker on 1, hits an unbelievable 7-iron to like 10 feet and holes the putt," McIlroy said. "People wouldn't maybe pick a Keith Mitchell to win a tournament at the start of the week, but you play with him in a final round on a Sunday, he stopped me in my tracks. I was like, 'He is a hell of a player.'
"People don't realize ... I mean, you could say that about 100 guys out there," McIlroy added. "That's the thing. You turn up to a PGA Tour event, you feel like three-quarters of the field have a chance to win."
The best chance this weekend belongs to Mitchell, who knows a thing or two about depth on the tour. Anyone can go low at any minute, especially in conditions like this.
Ian Poulter played with Mitchell and had rounds of 66-67. He was seven behind.
"We're trying to birdie every hole on the golf course, and you can't be any more aggressive than that," Poulter said. "It's just the first two rounds that Keith has played is pretty impressive. Eighteen under for two days is some good golf."