After missing a succession of makable putts, Mickelson's 5-iron at his 14th hole, the 190-yard fifth, headed straight for the pin, landed 12 feet short, bounced once and rolled into the hole.
"I was struggling to get the ball in the hole with the putter so I needed to hole from off the green," he joked, adding that he's had 15 to 20 aces as a professional.
"I don't remember the last one. It has been a little while."
Mickelson shot a 4-under-par 67 for the day and picked up one stroke on Cabrera, who had a 68 for a 9-under 133.
Cabrera bogeyed two of the last four, including the 18th, where he missed the green. "That was a shame but I'm happy with my putting and my swing," the Argentine said.
Mickelson finished his round with a birdie at the par-5 sixth hole - just missing an eagle
- and also at No. 9 from 12 feet. At 4-under 138, he was two inside the 36-hole cutoff.
"Seeing that last one go in gives me a little confidence because I didn't see any go in today. That gets me a little excited for the weekend," the American said. "I just need to get the ball to track in on the greens."
Cabrera led by one over Damien McGrane of Ireland, who shot 66. A group of five were two shots back, including overnight leader Thongchai Jaidee, former Open champion Paul Lawrie and Thomas Bjorn, who won this event when it was first played at Loch Loomed in 1996. Simon Khan and Richard Green were also two back.
Ernie Els also made progress, his seven birdies masking two bogeys and a weak finish in a 66.
"I'm not striking it 100 percent," said Els, who was tied with Mickelson five strokes back. "You could see that in my finish. Missed the fairway on seven and three-putted there, then had to make great up-and-downs at 8 and 9."
Els, like Mickelson, started at the 10th.
