His rushed par-save attempt ended up further past the hole than his original birdie attempt, with McIlroy requiring another two putts - taking his tally to four from inside six feet - to eventually nudge in a double-bogey six.
UPDATE NO. 1 (12:35 p.m. ET): Patrick Cantlay, Will Zalatoris, Beau Hossler, Kevin Streelman and Troy Merritt are all tied for the lead at 7 under.
Padraig Harrington, Shane Lowry and Seamus Power all begin at Monterey Peninsula while Graeme McDowell's first round is at Pebble Beach.
"I feel like there's nothing in my way", McIlroy said.
But going into Pebble Beach, he ranks 195th in the key putting statistic out of 206 players.
"I was just sort of ready to call it quits for the year after the Dunhill", he said.
Johnson said he's approaching the form that saw him win three straight tournaments early a year ago before he fell on some stairs and hurt his back as he prepared to tee it up in the Masters.
"I was happy with my round and anytime you can get it around Spyglass with a decent score you have to feel good as it is the tougher of the three courses", he said. "That was probably some of the best golf I've played in my career, but parts of the game are just as good".
Johnson's game is built around his driving prowess, ranking first in SG: off-the-tee (gaining 2.225 strokes over the field) and first in SG: total. That put him alongside Mickelson in the group of six players sharing fifth place on nine-under, which also included former world number one Jason Day who posted a six-under 65 at Monterey Peninsula.
He attempted a very long putt from the fringe, nearly sinking it for an eagle and putting it just six feet past the cup.
After two strong performances in the Middle East recently, albeit without a victory, he is eager to make the most of his good health.
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