Los Angeles - Rory McIlroy, making his first start as world number one since 2015, pulled within two strokes of 36-hole leader Matt Kuchar on Friday as Tiger Woods's hopes of a landmark Genesis Invitational win dwindled.
Northern Ireland star McIlroy fired six birdies in a four-under par 67 at Riviera Country Club, to share second place on seven-under 135 with Americans Harold Varner and Wyndham Clark, who both signed for 68s.
Kuchar, who started the day with a three-shot lead, posted a two-under 69 that put him at nine-under par 133.
Woods was nine shots off Kuchar's lead, tied for 45th, after a two-over 73 that included a double-bogey and three-bogeys.
"I made some bad mistakes out there," said Woods, who opened with a birdie at the 10th but soon found himself in trouble. "I had a wedge in my hand at 15 and made double there, sand wedge on three and made bogey there.
"Three runaway shots with wedges, something I rarely ever do," added Woods, who was in the fairway with 144 yards to the hole at 15 but found a greenside bunker on the way to a double-bogey.
He clawed back two shots with birdies at the 17th and first, but was in another greenside bunker at the third and couldn't get his seven-footer to save par to drop.
Two more bogeys in the next three holes further dimmed his chances of breaking Sam Snead's record of 82 PGA Tour victories this week.
Woods matched the record with a win at the Zozo Championship in Japan in October, and finished tied for ninth in his only other start since at Torrey Pines.
The record would be extra sweet this week at Riviera -- the course where Woods made his tour debut as a teenager, but where he has come up empty in 12 prior starts.
"I'm going to have to make some birdies this weekend," he said.
McIlroy, playing Riviera for just the fourth time, birdied all three par-fives and while he hit just four of 14 fairways he avoided major trouble.
"Most of the day I did the things that I needed to do," he said. "I missed a few fairways coming in and it makes it very difficult to control your spin and get any spin onto the ball coming into these greens.
"But I managed it well, played the angles, got a couple of really nice up-and-downs towards the end -- a nice two-putt on 18."
Kuchar, however, said his lack of accuracy had him on the defensive all day.
"Wasn't driving it nearly as accurate as I did the first day," said Kuchar, who made the first of his two bogeys at the par-five first.
After an 18-foot birdie putt at the third he rolled in a 20-footer from the fringe at the fifth, but a bogey at the seventh saw him make the turn even for the day.
Back-to-back birdies at 10 and 11 proved enough to give him a two-shot cushion.
"Two-under was an awfully good score for the way I drove it today," Kuchar said. "I better find more control."
Nineteen players were within five shots of Kuchar's lead.
Australian Adam Scott fired seven birdies in his seven-under 64 to share fifth place on 136 with South Korean Kang Sung and Americans Vaughn Taylor and Russell Henley.
Sung and Taylor posted 67s while Henley carded a 69.
Spain's Rafa Cabrera Bello and American Chez Reavie were tied on 137, while world number three Jon Rahm of Spain headed a group of 10 on 138 that also included defending champion JB Holmes, Justin Rose and Dustin Johnson.
Leading second-round scores on Friday in the US PGA Tour Genesis Invitational at Riviera Country Club (USA unless noted, par-71):
133 - Matt Kuchar 64-69
135 - Harold Varner 67-68, Rory McIlroy (NIR) 68-67, Wyndham Clark 67-68
136 - Kang Sung (KOR) 69-67, Adam Scott (AUS) 72-64, Vaughn Taylor 69-67, Russell Henley 67-69
137 - Chez Reavie 69-68, Rafa Cabrera Bello 68-69
138 - Jon Rahm 70-68, JB Holmes 69-69, Justin Rose (ENG) 69-69, Kim Si-woo (KOR) 69-69, James Hahn 68-70, Carlos Ortiz (MEX) 68-70, Dustin Johnson 72-66, Paul Casey (ENG) 69-69, Sebastian Munoz (COL) 69-69, Bryson DeChambeau 68-70
139 - Joel Dahmen 68-71, Luke List 71-68, Scott Piercy 70-69, Scott Brown 71-68, Brian Harman 70-69