Lydia Ko celebrates 18th birthday with the lead in San Francisco

Lydia Ko was no longer a 17-year-old phenom when she took the field at Lake Merced Golf Course for the second round of the Swinging Skirts LPGA Classic.

On Friday, the world No. 1 and defending champ, who celebrated her birthday with a one-shot lead over a trio of players that included 54-year-old Juli Inkster, is now 18. Other than that, nothing much had changed for the six-time LPGA Tour winner who, once again, had the rest of the competitors playing catch-up.

“I saw the leaderboard on, I think, 12 or 13. Just kind of laughed to myself to see her name up there again,” Stacy Lewis told reporters after notching a 5-under 67. “It’s not surprising. She loves this golf course. You kind of have to laugh, but then you kind of don’t because you expect her to be there.”

Inkster may have 36 years on the leader of the pack, but to Ko, who said recently she planned to retire by age of 30, it’s all just a numbers game.

“That’s why I think golf is a great sport; it doesn’t matter if you’re 10 or 20 or if you’re 60, everybody can play,” said Ko after signing for a 67. “What [Inkster has] done for the tour is pretty amazing. I think the tour, we’re getting more popular because of players like her that kind of showcased the LPGA throughout the years.”

A post-round dinner with friends was about all that would be different for the young lady who had not missed a cut in 49 previous starts on tour.

“I won’t change [my game plan] just because I’m one year older,” Ko said. “Really I’m only one day older tomorrow.”

Maybe so, but Ko and many of her peers are babes in arms compared with Inkster’s two offspring.

“Yeah, they’re a lot younger than my daughters [who are] 25 and 21. Out here that’s a seasoned veteran,” said the 2015 Solheim Cup captain after coming in with a 68 score. “You know what, that’s the beauty about golf. Age matters in a lot of things as far as how your body feels and how far you hit the ball and how much time you can put into it, [but] you can still go out there and compete at 54.”

Ko certainly appeared rested and ready after a two-week break following a disappointing T51 at the ANA Inspiration that her swing coach, David Leadbetter, blamed on fatigue. Indeed, Ko got right back in the swing of things, making consecutive birdies three times and almost chipping in for eagle on the par-5 14th.

“I didn’t feel too tired after ANA but other people said I looked it on TV,” Ko said. “It just shows a sign that I needed that break and I definitely think it was worth it.”

Also free from fatigue was hometown legend Inkster, a native of nearby Santa Cruz who has a house full of LPGA players this week at her nearby residence.

Mountain View-born Paula Creamer was also playing on home turf but her large gallery of family and friends probably won’t get to cheer for her over the weekend. The 2010 U.S. Women’s Open champion, who’s made news recently with her calls for a Women’s Masters at Augusta, carded four bogeys and two triples on her way to an 82.