The 25-year-old, who claimed his maiden European Tour title in Hong Kong two years ago, produced a three-under third round to advance to eight under for the week in Ballymena.
Rai held a one-shot overnight lead but was joined at the top when Australian Maverick Antcliff completed his delayed second round with an eagle on the 18th.
The 27-year-old Antcliff then holed a putt from the fringe for a birdie at the first to go ahead as Rai bogeyed the opening hole.
However, Rai made three gains in five holes from the third and, with Antcliff bogeying the second and sixth, regained an advantage which he maintained with two birdies against a single dropped shot on the back nine.
“I’m pleased with the round overall,” said Rai. “It wasn’t easy, the course isn’t playing easy and it wasn’t easy conditions today.
“It’s always different going out in the final group and with the co-lead on day three, so it’s nice to play with that and play relatively freely and solid today.
“It would be incredible [to win]. Any title on the European Tour is fantastic, the Irish Open has an illustrious history, it’s a huge event, it always has been.
“I want to put that out of my mind going into tomorrow. There’s still a lot of significance to it, but I’ll hope to do the same kind of things and see where it puts us at the end of tomorrow.”
Sweden’s Oscar Lengden, Thailand’s Jazz Janewattananond and South African Dean Burmester share third on six under par.
