AP photo by Charles Krupa / Phil Mickelson hits out of the woods attempting to reach the 14th green at TPC Boston during the second round of The Northern Trust on Friday in Norton, Mass.

SPRINGFIELD, Mo. — Phil Mickelson would much rather have been playing in the final round of The Northern Trust on Sunday, not only because he believes his game is rounding into shape but because it might mean he was still alive in the PGA Tour's FedEx Cup playoffs.

Plus, he would be able to continue a nice ramp-up toward the U.S. Open, set for Sept. 17-20 at Winged Foot Golf Club in Mamaroneck, New York.

Fortunately for Mickelson, though, he celebrated his 50th birthday in June

Such a milestone might bring a shudder to many folks, but it actually worked out quite nicely for Lefty. It grants Mickelson access to the PGA Tour Champions, and that means he can keep fine-tuning his game when he makes his debut on the 50-and-older circuit Monday at Ozarks National, the course hosting the second of back-to-back 54-hole senior tournaments at Ridgedale's Big Cedar Lodge resort.

"I didn't really want two weeks off. I've been working hard on my game. I want to get out and play, so this worked out really well," Mickelson said. "It's such a beautiful place. I'm a big fan of Bill Coore (and) Ben Crenshaw golf course designs, and we are here playing one of the best. And it's a beautiful area, so I'm excited to compete."

Mickelson was just inside the playoff cut line heading into the opener at TPC Boston, but a first-round 74 took him out of contention for playing the weekend. It also took him out of the BMW Championship that starts Thursday at Olympia Fields Country Club near Chicago and shot down any hopes of making the following week's Tour Championship, the PGA Tour's 2019-20 season finale at Atlanta's East Lake Golf Club.

That left him only the Safeway Open on the PGA Tour schedule before heading to the season's second major championship, where the five-time major winner will take another shot at completing a career Grand Slam after six runner-up finishes in the U.S. Open. Rather than sulk about his lack of opportunities on the main circuit, Mickelson hopped a plane to the Ozark Mountains of southwest Missouri, where he found himself among plenty of familiar faces for the second event in the two-tourney Charles Schwab Series.

Fellow tour rookies and former major champions Ernie Els and Jim Furyk, both of whom already have won this season, are in the field at the picturesque course at Big Cedar Lodge, and so are 2003 Masters winner Mike Weir and K.J. Choi, who won The Players Championship in 2011. Mickelson will be paired with good friends and longtime rivals Steve Stricker and Retief Goosen, a two-time U.S. Open winner.

"I haven't seen them in a long time," Mickelson said. "Grew up playing with them for a number of years, and it's exciting for me to come out here and see so many people I know. On the regular tour, I don't know a lot of the guys now."

Mickelson had a roller-coaster season on the PGA Tour, with the ups including finishing second at the World Golf Championships' FedEx St. Jude Invitational early this month and third at the AT&T Pebble Beach Pro-Am in March. He also made the cut at the recent PGA Championship at TPC Harding Park in San Francisco, though he faded well off the pace over the weekend. He also has missed six cuts, including at The Northern Trust, leaving him with both optimism in his game and clearly defined areas that need work.

"I love playing and competing, and heading into the U.S. Open, I'll play the week before in Napa, but I didn't want to have two weeks off when I've been working hard on my game," he said. "I was really wanting to play and compete in the playoffs, so it was a disappointing first round, and it's fun for me to have a chance to come play."

Fun for tournament organizers, too. There is a sudden buzz that was lacking just days ago, when the PGA Tour Champions played the neighboring Buffalo Ridge course in an event won by Shane Bertsch in a four-man playoff.

"Phil's had an amazing career and still plays at a very high level. It's great to have him out here," said two-time Masters champion Bernhard Langer, the 62-year-old German star whose 42 senior victories rank second on the all-time list. "I'm sure any tournament or any sponsor will be happy to see Phil. It's great the guys who have come out lately with Ernie Els, Retief Goosen, Mike Weir and on and on."

Mickelson would love to win this week. He never goes into a tournament expecting anything less. But he also wants to make sure his game is in shape for Winged Foot, the course just north of New York City where Furyk, Mickelson and Stricker were part of a five-way tie for second in the 2006 U.S. Open won by Geoff Ogilvy.

"Well, it will be fun and exciting to compete at Winged Foot," Mickelson said. "It's been 14 years since I've been back there, so I'm looking forward to getting back and playing a golf course that I was so close to accomplishing a dream."