McIlroy retained his share of the lead with Day, who played alongside McIlroy, posting the lowest round of the day, an eight-under par 64 to move into second place at eight under par.
18th hole leader board after two rounds of the 2011 Masters
Four-time Masters winner Tiger Woods roared into contention with nine birdies, including a gem up the last when he was behind trees up the right side of the fairway, and then ‘cut’ an 8-iron to 12-feet.
Woods signed for a 66 to be tied in third place with Korean K J Choi bogeyed the last in a 70.
Two players, Australia’s and former US Open winner, Geoff Ogilvy (69) and Spain’s Alvaro Quiros (73) sharing fourth spot on six under par.
Korean Y E Yang (72) along with 1992 Masters winner Fred Couples (68) are in a group on five under par with Mickelson signing for a 72 to remain at two under par.
The 21-year old McIlroy grabbed four birdies in his round, including a 12-foot gem at the par five second hole, along with just a single bogey at the infamous par three, 12th hole where he found the bunker in front of the green.
Rory McIlroy - Retains his share of the lead. (Pic - European Tour)
It has put McIlroy on the verge of becoming the second youngest winner of the Masters.
Tiger Woods was 21 years, 3 months and 14 days old when he scored a ‘win for the ages’ in capturing a first Masters in 1997 by a dozen shots.
Seve Ballesteros had been the youngest winner of the green jacket in 1980 when he was aged 23 years and 4 days old.
Six-time Masters winning Jack Nicklaus was fitted for his first Masters green jacket in 1963 and four years after making his debut.
The Golden Bear was 23 years, 2 months and 17 days old.
While if Day should win he will be 23 years, 4 months and 28 days old in becoming the first Australian ever to be fitted for the green jacket.
McIlroy already created history this year in becoming the youngest ever player to lead the first round when he and Spaniard Alvaro Quiros shot first round 65s.
Now after 36-holes he’s dropped just one shot in 36-holes.
“The key in major championships is to really limit your mistakes and I’ve been able to do that over the first couple of days,” he said.
“To make just one bogey in 36 holes around this golf course, it’s very satisfying.
Two round totals of all 2011 Masters participants
“Of course, it would have been nice to be bogey‑free, but I’m happy with where I’m, and my game feels really good.
“It’s been great playing with Rickie (Fowler) and Jason (Day) and I think collectively for the last two days we are 23‑under par.
“We played some really good golf out there, and we fed off one another, and we got a bit of momentum early and the crowd got behind us on the back nine and really pushed us along.
“So we all really enjoyed it out there, and hopefully there’s more to come over the weekend.”
Mickelson kept his hopes alive of joining arch-rival Tiger Woods in capturing a fourth green jacket with four birdies in a level par 72 to remain at two under par.
Phil Mickelson promises McIlroy a fight
And last week’s Shell Houston Open winner, who already has three green jackets in his wardrobe, says McIlroy
“Rory’s playing great and he’s a great player, so it’s no surprise at all,” he said.
“He hits the ball long and I expect him to play well on this golf course throughout his career, and it’s not a surprise.
“But there’s still a lot of golf left in this tournament and I’m going to be making a run at him and the other guys ahead of me here on Saturday.”
And when Mickelson was quizzed where he does he draw his confidence he said: “Three green jackets.”
Bernie McGuire at Augusta National.
