Phil Mickelson was in high school the only other time PGA West's TPC Stadium Course was used in what is now called the CareerBuilder Challenge.

Ready or not after a long layoff and swing changes, Lefty had a prime Saturday tee time on the Pete Dye-designed course that was dropped from the tournament rotation after its 1987 debut.

"I'm probably a week away, if I'm being honest," Mickelson said Friday. "But I've also won with a lot less game than I have right now."

Playing his first event since October and first since splitting with swing coach Butch Harmon to work with Andrew Getson, the 45-year-old Mickelson opened with a 4-under 68 on Thursday at La Quinta Country Club and shot a 65 on Friday on the Nicklaus Tournament Course. The Stadium Course had a stroke average of 71.029 in perfect scoring conditions the first two days, nearly two shots higher than the Nicklaus and La Quinta layouts.

"I'm looking forward to the challenge and having to really focus on every tee shot to get it in play," Mickelson said Friday "But I hit a lot of good shots today on crucial tee shots and was able to get it in play. If I hit it the way I've been hitting it, driving it in play, I think there's a lot of birdie opportunities still."

Winless since the 2013 British Open, the 2002 and 2004 champion was four strokes behind leader Jason Dufner.

"I feel like I'm on the right path with the right direction," Mickelson said.

Dufner knows his way around the Stadium and Nicklaus courses. He learned out of necessity at the 2008 PGA Tour qualifying tournament.

"I probably played each four or five times before that Q-school started," Dufner said. "I played unbelievable. I think I shot 24 or 25 under for the six rounds. And to be honest with you, this is kind of where everything started for me, because then in 2009 I had a really nice season."

He shot a 65 on the Stadium Course on Friday to take a one-stroke lead over Jamie Lovemark.

"It's a difficult golf course," Dufner said. "There's a little bit of room to play off the tee, but if you get off the path a little bit, you can get into some trouble. ... It's definitely the most difficult of the courses we have played here."

Dufner parred the final four holes, escaping trouble on the par-5 16th after his drive strayed to the left. The 2013 PGA Championship winner played the front nine in 6-under 30, bogeyed the 10th after hitting into the greenside water, and added birdies on 12 and 14. He was forced to lay up on all four par-5 holes and took advantage of many short approach shots.

"Any time I'm inside of 130 yards I feel pretty good," Dufner said. "I had some really good numbers with my wedges, which helps."

Dufner's drive on 16 perched on a ledge of dormant grass above one of the deep bunkers that line the left side. The ball at knee level, he slashed it 100 yards down the fairway before slipping to his hands and knees on the steep bank.

"I thought I would have a good go at that green in two and maybe get another birdie or possibly even an eagle and walked away with a 5, but no damage done," Dufner said.

He had only 22 putts, one-putting 11 of 12 greens in the middle of the round.

Dufner had a 15-under 129 total. He opened with a 64 on Thursday on the Nicklaus Course, will play La Quinta on Saturday, and return to the Stadium Course for the final round Sunday.

Lovemark had a 65 on the Nicklaus Course. He holed out from 105 yards for eagle on the par-4 first, his 10th hole of the day.

"Got a little tired coming down the stretch," Lovemark said. "There's some long rounds out here."

Defending champion Bill Haas was three strokes back along with Jason Gore, Anirban Lahiri, Andrew Loupe and Adam Hadwin. Haas shot 66, Gore 64 and Lahiri 68, all at the Nicklaus Course. Loupe had a 66 on the Stadium Course, and Hadwin a 66 at La Quinta.

DIVOTS: Chesson Hadley made a double-bogey 5 on the island-green 17th on the Stadium Course after trying to hit out of the rocks and going into water, then holed out from 142 yards for eagle on 18. He shot 73 and was tied for 113th at 2 under. ... Nick Taylor had a hole-in-one on the 205-yard sixth on the Stadium Course. He was tied for 70th at 5 under after a 69. ... Patrick Reed, the 2014 winner, was tied for 54th at 6 under after a 69 on the Nicklaus Course.