MEMPHIS, Tennessee, June 9, 2012 (AFP) - The Northern Ireland star, ranked second in the world, led by a stroke when the day began after an impressive 65 on Friday but made six bogeys against four birdies in round three at TPC Southwind to share second on a tight leaderboard.
"It was a very testing day with the conditions," he said. "I definitely didn't feel as comfortable with my game as I did yesterday.
"So, you know, it was a good experience for me just to try and do what I've been working on in my swing and under real competitive pressure.
"For the most part, I held up pretty well. Few missed shots out there. I'm only one off the lead and still in a good position."
Australian Nick O'Hern birdied the 14th, 15th and 16th holes to fire a 67 and grab a share of the overall lead at six-under par 204 alongside US veteran Davis Love and American John Merrick.
McIlroy, tuning up for defending his first major crown next week at The Olympic Club in this year's Open, was on 205 with Australian Robert Allenby and Americans Dustin Johnson, Chad Campbell, Kevin Kisner and Kevin Stadler.
McIlroy birdied the par-four second but answered with a birdie at the next hole. McIlroy took another bogey at the par-four fifth but responded with a birdie at the par-three eighth, only to take bogeys at the next two holes.
A birdie at the par-four 12th was followed by bogeys at the par-four 13th and par-four 15th but a closing birdie helped lift McIlroy closer to the top.
"It was a tough day," he said. "It was a day where, you know, for me I took one step forward and two steps back. Every time I made a birdie, I followed it up with a bogey.
"I'm only one off the lead. I'm fortunate I'm only one off the lead. Just going to go out there and give it a good one."
USA Ryder Cup captain Love says his form is back to where it was before injuring a rib muscle earlier this year at Bay Hill.
"Is it a big huge deal in my career that I have to win this week? No," said Love. "But when you get up there at the top ... the old feeling kicks in. You concentrate better, you focus better and my routines of the day were coming down those last four, five holes.
"And I missed a couple putts, but I felt like I was right in like old times."
"So it would mean a lot to win for sure. Anytime you win out here is important. But it's fun to be in it."
Leading scores on Saturday after the third round of the $5.6 million St. Jude Classic (USA unless noted):
204 - Davis Love 68-68-68, John Merrick 66-69-69, Nick O'Hern (AUS) 70-67-67
205 - Robert Allenby (AUS) 68-70-67, Chad Campbell 68-67-70, Dustin Johnson 70-68-67, Kevin Kisner 69-66-70, Rory McIlroy (NIR) 68-65-72, Kevin Stadler 69-65-71
206 - J.B. Holmes 70-64-72
207 - Woody Austin 72-68-67, Roberto Castro 73-68-66, Luke Guthrie 69-71-67, Padraig Harrington (IRL) 68-68-71, Fredrik Jacobson (SWE) 69-72-66, Jeff Maggert 66-68-73, Dustin Morris 71-69-67, Jeff Overton 67-72-68, Ryan Palmer 74-66-67
208 - Daniel Chopra (SWE) 72-65-71, William McGirt 71-69-68, Seung-yul Noh (KOR) 67-69-72, Henrik Stenson (SWE) 72-66-70