RIDGEDALE, Mo. -- Just about the only poor shot Phil Mickelson hit in his PGA Tour Champions debut was a wayward iron off the tee.
He still turned it into a birdie.
It was one of five straight on the back nine Monday for the five-time major champion, who decided to make his over-50 debut this week after missing the cut at The Northern Trust and getting eliminated from the PGA Tour's FedEx Cup playoffs.
Mickelson finished with 11 birdies and shot a 10-under 61 to take a 1-shot lead over David McKenzie in the Charles Schwab Series at Ozarks National.
"It's a lot of fun. It's a fun environment. And it's fun to see a lot of the guys I grew up watching, and played with them for a number of years, and played a bunch of Ryder Cups and Presidents Cups with a lot of of guys out here," Mickelson said. "I was a little nervous, too, because I wanted to come out and play well. I was playing really well."
K.J. Choi, making his second start on the PGA Tour Champions, was joined in a group at 7 under by Rocco Mediate, Rod Pampling and Tim Petrovic. Ernie Els, Bernhard Langer and Vijay Singh were among those another shot back.
"We have a lot of golf left," said Mickelson, who hit all but one green in regulation. "A lot of players went really low. The quality of golf out here is really impressive."
Mickelson, who turned 50 in June, was optimistic that his game was rounding into shape for the U.S. Open, the only major championship he hasn't won. But that missed cut on the PGA Tour left him with the possibility of not playing the next two weeks heading into the Safeway Open, which would be his final tuneup for Winged Foot.
So, the Hall of Famer hopped a jet to southwest Missouri and Ozarks National. The course is the new jewel of Big Cedar Lodge, the resort created by Mickelson's good friend and Bass Pro Shops founder Johnny Morris. With wide fairways and big greens, it hardly presents the challenge of Winged Foot. But it gave Mickelson a chance to fine-tune his game.
Paired with buddies Steve Stricker and Retief Goosen, he was among the last to go off Monday. But he wasted no time in starting to chase down McKenzie, who had posted a career-low round early in the day. Mickelson made birdie at the first, added four more over the next six holes, and had another birdie at the par-4 11th to offset his only bogey.
Then his putter caught fire on the tumbling, pristine greens.
Mickelson rolled in a short birdie putt at No. 13, then another at 14, before his iron off the tee found the fairway bunker at the par-4 15th. With the ball below his feet, Mickelson hit a solid approach to 40 feet left of the hole, then ran it in for a third straight birdie. He added two more birdies before missing a 15-footer at the last to shoot 29 on the back nine.
The record for birdies in a round on the PGA Tour Champions is 12.
"I was just trying to figure out a way to play this golf course smartly," said Mickelson, who has made 11 birdies in a round on the PGA Tour only once -- at the 2013 Phoenix Open, when he fell a lip-out short of shooting 59. "There's plenty of room if you find the right club."
McKenzie found the right club all day, too. The Australian made back-to-back birdies to finish the front nine, then rattled off three in a row on the back to shoot 62.
"I made a lot of putts today, which makes it a lot easier," he said, "but it has a little bit of a feel like Australia. I think it's Bill Coore, Ben Crenshaw that designed it, so I just like the way that it sits and feels. It's a really comfortable golf course."