America's Reed eagled both par-5 holes on Augusta National's back nine on Saturday en route to a five-under par 67 and, at 14-under 202, a three-shot lead over Northern Ireland star McIlroy.
McIlroy, a four-time major-winner who only needs a green jacket to complete his collection of Grand Slam titles, had five birdies and an eagle in his 7-under 65 for 205 -- and said he would be ready to swing away come Sunday.
"All the pressure is on him," McIlroy said. "He's got to go out and protect that, and he's got a few guys chasing him that are pretty big-time players. He's got that to deal with and sleep on.
"I can go out there and play like I've got nothing to lose ... I can go out and sort of free wheel."
McIlroy has been hankering for a return to the last group on Sunday at Augusta since 2011, when he took a four-shot lead into the final round and carded an 80.
Since then he has won four majors, but never a Masters.
"I've been waiting for this chance," McIlroy said. "I always have said that 2011 was a huge turning point in my career. Now I'm ready."
Reed, who is seeking his first major title, hinted that McIlroy's bid to become just the sixth player to win all four of golf's major championships carried it's own pressure.
"You can put it either way," Reed said, adding that he "felt fine" after sleeping on the halfway lead.
"I believe that's how it's going to be ... Wake up and just come out and play golf."
The needling was no surprise given their history – specifically Reed's 1 up victory, secured with a birdie at 18, which set the tone for the US Ryder Cup victory over Europe.
Both Reed and McIlroy, however, said it would be dangerous to go into Sunday with eyes only for each other.
American Rickie Fowler and Spain's Jon Rahm matched McIlroy's 65 on Saturday, Fowler heading into the final round five shots off the lead and Rahm one stroke behind him.
Sweden's Henrik Stenson, a British Open champion, is seven adrift and two-time Masters champion Bubba Watson is eight shots off the lead.
"There's a lot more players in this golf tournament than just Patrick Reed and I," McIlroy said. "It's definitely not a two-horse race at this point."
McIlroy believes his nine prior Masters appearances have earned him some support around Augusta, while Reed led Augusta State to two national collegiate golf championships in 2010 and 2011.
"It's going to be awesome to come out tomorrow and have a lot of Augusta State guys out here cheering me on," Reed said – although he noted that the stately confines of Augusta National would make for a far different experience than a rowdy Ryder Cup.
"There's a lot of stuff that you can do at Ryder Cup that you can't do at Augusta National," he said.