(Reuters) - Former champion Matt Kuchar continued his love affair with the Memorial tournament on Friday as he took advantage of calm conditions with a late birdie flurry to surge into a two-way tie for the lead in the second round.

Kuchar birdied four of his last six holes to shoot a sparkling six-under-par 66 at Muirfield Village, finishing level with fellow American Brendan Steele (67) at 12-under 132.

Argentina's Emiliano Grillo (66) and long-hitting American Gary Woodland (65) were at 11-under while Australian world number one Jason Day followed his opening 66 with an erratic 71 to drop five strokes off the pace.

U.S. Open champion Jordan Spieth and Rory McIlroy both put mediocre first rounds behind them as they moved into contention, American Spieth carding a 68 to finish at six-under, a stroke behind Northern Irishman McIlroy who returned a 66.

Kuchar, who won the 2013 Memorial tournament and has recorded four top-10s in his last five PGA Tour starts, was delighted to benefit from another benign day at Muirfield Village in the prestigious event hosted by Jack Nicklaus.

"I've been in some great form," the 37-year-old told reporters after mixing seven birdies with a lone bogey. "Nice to keep it going.

"The course is in fantastic shape ... it's as easy at this place as I remember ever seeing it, even though the greens are still fast.

"You can get in the wrong spot, but you don't have to worry too much about the wind. It's fun to be out there playing and making some birdies around this place."

Kuchar, a seven-times winner on the PGA Tour, has always enjoyed competing at Muirfield Village.

"I've certainly had a great track record here ... winning in 2013, and a lot of nice solid finishes," he smiled. "It's certainly been a nice Thursday, Friday start, and I'm looking forward to a great weekend."

Day was also looking forward to a great weekend after relying on his deft touch around the green and scrambling abilities as he eked out a 71 that included five birdies and four bogeys.

"If I didn't have a short game, I probably would have shot high 70s," said the Australian, who clinched his third PGA Tour victory of the season at the Players Championship last month.

"But to be able to stick it out and shoot one under on a tough day like this was pretty nice."

Spieth was flirting with the cutline after he bogeyed two of his first four holes but he picked up six shots over the closing stretch to vault up the leaderboard.

"Six birdies in 12 holes, that's one every couple holes," said the 22-year-old Texan. "That's a nice ratio out here. I felt like I had enough chances to get in a rhythm with the putter."

American Dustin Johnson, who fired an eight-under 64 to seize a one-shot lead after the opening round, ended the round three strokes off the pace after carding a 71.

(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Andrew Both)