DALY CITY, Calif. (AP) — Lydia Ko twice thought someone else would leave Lake Merced with the trophy this year.

She was on the putting green listening for a cheer if Morgan Pressel were to make a 15-foot birdie putt in regulation to win the Swinging Skirts LPGA Classic.

Ko heard nothing.

In a playoff, she could only watch as Pressel stood over a 10-foot birdie putt for the win.

It grazed the edge of the cup.

With the tournament finally in her capable hands, Ko rolled in a 5-foot birdie putt on the 18th hole to beat Pressel on the second playoff hole and cap off another birthday week in style. She turned 18 on Friday and is only getting better.

She played the par-5 closing hole at Lake Merced three times and made birdie twice, the first one an 8-foot putt in regulation for a 2-under 70 that set up the playoff. Pressel played it three times and made par. Knowing that Ko was in tight for a likely birdie on the second playoff hole, Pressel missed from 8 feet.

The finish was inevitable. If the South Korean-born Kiwi isn't winning, she's always around the top of the leaderboard. Given one too many chances, Ko converted.

"It's always a close one whenever I play this event," Ko said. "Last year was the first time that every little shot counts."

A year ago, Ko had to make a 6-foot birdie putt on the par-5 18th to hold on for a one-shot victory. This one was even tighter, and Ko had reason to believe this wouldn't be her week when she followed a 40-foot birdie putt on the par-3 15th by making a sloppy bogey on the 16th and missing a 6-foot birdie putt on the 17th.

"I said, 'If I want to put some pressure, I need to make a birdie or better on 18,'" Ko said. "Ended up being good for that. But yeah, this tournament always makes my heart clench. I got so nervous. It's a good thing they're going in the hole."

It was a tough loss for Pressel, whose last victory was in 2008 at the Kapalua LPGA Classic. She had a two-shot lead with four holes to play until making back-to-back bogeys, and then failing to make a birdie on the 18th.

The par-5 closing hole could not be reached in two, so it effectively came down to a wedge and a putt.

"I just couldn't convert the putts," Pressel said. "It all comes down to putting. She birdied it twice and I didn't."

Brooke Henderson, the 17-year-old Canadian, holed a bunker shot for eagle on the par-5 14th to stay close to the lead and she had a 25-foot birdie putt on the final hole to join the playoff. It missed on the low side and she had to settle for a 74.

Ko, already the No. 1 player in women's golf, moved to the top of the LPGA Tour money list with her second LPGA Tour win this year. But it was hard work. She opened with a pair of bogeys. She never had the lead until making her winning putt on the 20th hole of the day.

"At the start of the day, I didn't know how it was going to go," Ko said. "It's been a great birthday week again."

Ko, who matched Pressel at 8-under 280, earned $300,000.

She played slightly more aggressively the third time around on the 18th, going with a 3-iron hybrid on her second shot that allowed her to close the face on a 54-degree wedge and swing hard, instead of easing off a pitching wedge the previous two times. It paid off for her.

Henderson made two bogeys in three holes to fall out of the lead for the first time since Friday morning. The Canadian never caught up, though she was never out of it until missing her birdie putt on the final hole.

"It was one of the least nervous putts I had all day," Henderson said. "I could see it going in in my mind, but it didn't happen in real life."

She headed for Texas to try to Monday qualify for the next LPGA event. Finishing in the top 10 only makes a player eligible for the next tournament if she is an LPGA member. Henderson last year was denied a waiver to the LPGA's minimum age requirement of 18.

Pressel took the lead by making pars, and she started to seize control when she rolled in a 45-foot eagle putt on No. 6 for a two-shot lead. But she missed three short putts on the front nine — two for birdie, one for par — that kept her from getting a little more separation.

The final hour took shape with three big shots. Henderson holed her bunker shot for eagle on the 14th to reach 8 under and get within one shot of the lead. Moments later, Pressel got up-and-down from behind the green to get to 10 under and, in the group ahead of them, Ko made her big birdie putt to reach 8 under.

But then it got messy.

Pressel dropped shots on the next two holes. Henderson chunked a chip on the 15th and made bogey. Ko went well long on the 16th and missed a 10-foot par putt.

Ko said she was nervous. It just doesn't show.

"At her age, she plays with so much poise and calmness I don't think you see from other kids her age," Pressel said, pausing before she added with a smile, "I guess she's not a kid anymore."