She couldn't, and the double bogey saw her sign for a 73 and a share of second, and the best opportunity she's had in years to win a tournament disappear.
Here's how the dramatic final round unfolded:
10.06am - Kang wins by one shot. Not really sure what we just witnessed. 90 minutes ago Ko was looking odds-on to get her first win since 2018. She was playing confident golf but then it all fell apart on the back nine. Dropped shots at the 14th and 16th hole saw her lead evaporate to just one shot on the 18th tee but no one would have expected a double bogey finish. Kang didn't need to do too much on the last four holes with pars in all of them but it was enough for the victory.
10.01am - 18th hole: Double bogey for Ko. And Ko loses it with a double bogey seven on the easiest hole on the course. Kang wins her second straight tournament. A shocking way to finish for Lydia. She had a five shot lead with six holes to play and still held a one shot lead on the 18th tee.
9.58am - 18th hole: Ko putting for bogey. Ko has a shocker and her chip rolls into the bunker. She takes five to get on the green.
9.55am - 18th hole: 3rd shot. After taking an age, Ko's approach goes through the green and ends up in the rough right next to Kang in the bunker. And then Kang can't get on the green either landing in the rough short of the green.
9.45am - 18th hole: 2nd shot.Both go for the green. Ko goes wide and finds the cart path again. But Kang finds the greenside bunker and will have a very tough bunker shot. She might have to stand outside the bunker in her stance. Ko will drop off the cart path.
9.40am - 18th hole: 1st shot. A big sigh of relief as Ko walked off the 17th green with a par. She drills the drive up the last hole down the fairway. Kang also with a big drive and is safe. It's a par five so these second shots will be crucial.
9.36am - 17th hole: Par for Ko. Ko manages to walk away with par and is even for the day. Kang just misses a birdie putt and Ko still leads with one to play. Ko -16, Kang -15.
9.34am - 17th hole: Ko in trouble. Ko has to chip on with her fourth while Kang is also chipping but it's her third shot.
9.24am - 17th hole: Wayward driver. Could it be falling apart for Ko? Her drive on the 17th goes wide ride and lands near a cart path. Kang meanwhile smashes her driver down the fairway.
9.22am - 16th hole: Bogey for Ko.
Ko drops another and it's now a one shot lead with two par fives remaining. Both players went too hot with their drives and found the rough. Ko then went into the greenside bunker and didn't have much green to work with. That left a long par putt which went around the lip. Kang meanwhile walks away with par. Ko -16, Kang -15, Jodi Ewart Shadoff now at -14 still in play as well.
9.03am - 15th hole: Par for Ko.
Kang misses a chance to make it just one shot. A nice recovery from Ko after finding the fairway bunker left. She manages to get on the green and two putt for par. Kang misses an eight footer for birdie. Lead remains two with three to play. Ko -17, Kang -15
8.51am - 14th hole: Bogey for Ko.
Oh dear. A four shot lead is now two! Ko finds the first cut at the back of the green and has to chip on. But she leaves a decent par putt which she can't drop. Kang meanwhile puts her tee shot just past the hole and sinks the birdie. What was a five shot lead a hole ago is now two. Ko -17, Kang -15
8.44am - 13th hole: Par for Ko.
Sixth par in a row. Ko's lengthy birdie putt falls short and she's left a two-putter for par which she sinks. Kang does pick up a shot with a birdie. Lead now four with five to play.
They head to the 14th where Ko had a bogey yesterday. Though expect a strong finish for the Kiwi. Ko is six-under through the final three holes this week. Ko -18, Kang -14
8.32am - 12th hole: Par for Ko.
All looking good for Lydia. Another tap-in par for Ko as she remains at -18. And Kang misses a six-footer and makes bogey. Lead now five with six to play. Ko -18, Kang -13, Ewart Shadoff -13
8.19am - 11th hole: Par for Ko.
Both Ko and Kang find the front of the very tough 11th green, the hardest on the course. Ko's ball actually rolls off and she needs to chip but it's a great effort and she taps in for par. Kang also recovers well to get a two-putt par. Ko -18, Kang -14 A hole ahead Jodi Ewart Shadoff moves to -13.
8.05am - 10th hole: Par for Ko.
Ko leaves a long birdie putt and results in a tap-in for par. Kang also walks away with par after a deft chip from the rough. Lead remains at four with eight to play. Ko -18, Kang -14
PGA Championship update: Still an hour away until the leaders tee off but some low scores early on setting it up for a wild finish to the first major of the year. Already two scores of 64 in the clubhouse.
7.51am - 9th hole: Par for Ko.
First mistake of the day as Ko finds the fairway bunker with her drive. The approach finds the rough wide right and then the chip to the green leaves a 10 footer for par. Which she makes for a great recovery. Kang picks up a birdie though and cuts the lead back to four. Could have easily been two shots earned there. They head to the back nine.
1 - Lydia Ko (NZL) -18 (through 9)
2 - Danielle Kang (USA) -14 (9)
3 - Jodi Ewart Shadoff (ENG) -12 (10)
4 - Minjee Lee (AUS) -12 (10)
7.37am - 8th hole: Par for Ko.
Kang drops a shot and the lead now for Ko is five. At the par three eighth, Kang finds a bunker and can't scamble from there. Ko finds middle of the green and misses the birdie putt but taps in for a five shot lead. Ko -18, Kang -13
7.26am - 7th hole: Birdie for Ko.
On the par five off the tee Ko finds middle of the fairway and then lays up for a short wedge approach to the green. She doesn't get as much backspin as she wants and is left with an 18-footer downhill putt for birdie. And she sinks it! Kang also leaves with a well-earned birdie after a wayward drive. Ko -18, Kang -14.
7.12am - 6th hole: Par for Ko.
Ko gets a nice kick onto the green which sets up a birdie putt from nine feet. But the putt breaks right late and she taps in for par. Kang makes par after a long birdie putt falls short. Ko -17, Kang -13.
7.01am - 5th hole: Par for Ko.
Ko has an eight footer for par and drains it. Kang makes a similar putt for par to remain at -13. The Kiwi's lead remains at four as they head to the par three sixth.
1 - Lydia Ko (NZL) -17 (through 5)
2 - Danielle Kang (USA) -13 (5)
T3 - Minjee Lee (AUS) -11 (6)
T3 - Jodi Ewart Shadoff (ENG) -11 (6)
6.47am - 4th hole: Par for Ko. Another par for Ko at the par four fourth hole sees her remain at -17 and hold that four shot cushion. Kang remains at -13 and Lee at -11. No treats surging up the leaderboard either.
6.35am - 3rd hole: Birdie for Ko. Ko picks up her first birdie of the day at the par four third to move to -17. Kang also birdies the hole and remains four back at -13.
1 - Lydia Ko (NZL) -17 (through 3)
2 - Danielle Kang (USA) -13 (3)
3 - Minjee Lee (AUS) -11 (4)
4 - Jodi Ewart Shadoff (ENG) -10 (4)
5 - Lindsey Weaver (USA) -9 (4)
6.25am - 2nd hole: Par Second straight par for Ko as she fails to birdie the par three for the fourth straight time. Kang does though, bouncing back from the early bogey and reduces the lead back to four shots.
6.15am - 1st hole: Par Ko begins the final round with a par on the opening par four. Her lead is extended to five shots though as playing partner Danielle Kang picks up a bogey. Ko now heads to the par three second, the only hole she has birdied all three days so far.
6am - European Tour: Ryan Fox has had another top 20 finish on the European Tour after finishing in a share of 19th at the English Championship (not to be confused with the Open Championship or the British Masters or the UK Championship). Fox shot an even par 71 to end up a staggering 14 strokes back from winner Andy Sullivan.
5.55am - PGA Championship update: The leaders don't tee off for a few hours at TPC Harding Park but Kiwi Danny Lee was out early. He's one-over for the day through 12 holes and sits in a share of 73rd. It's a very Danny Lee-like one-over as well with four bogeys and three birdies.
5.45am - Early scores: Looks like we could expect some low numbers today. Former world number one Stacy Lewis has carded a six-under 65 to move to a share of eighth, still nine back from Ko. Fellow American Andrea Lee has also shot a 65 to finish at eight-under. Ko set to tee off at 6am NZT.
Preamble: Ko is a round away from returning to the winner's circle on the LPGA Tour. Ko, who hasn't claimed victory since April 2018, holds a four-shot lead going into the final round of the Marathon Classic in Ohio.
Tied for the lead after the opening round and ahead by one through two low-scoring rounds, Ko produced a steady three-under par round of 68 yesterday to move to 16-under and extend that advantage to four over Danielle Kang.
She's aiming for her third win at the Marathon Classic after victories there in 2014 and 2016.
The winner's share of the tournament's US$1,850,000 prize pool is a cool US$277,500 (NZ$420,000).
