The emergence of a new star and the sad stumble of a former world number one feature in AFP Sport's golf talking points this week:

The elevation of 23-year-old US PGA Champion Collin Morikawa into golf's top echelons has been as relentless as it has been rapid.

The game's latest major force only graduated from UC Berkley in May last year and turned pro after a prolific college career.

His record since on the PGA Tour is stunning -- three wins, two second places, three other top-10s and only one missed cut in 28 events.

Only Tiger Woods boasts a better record than Morikawa's 22 straight weekends played to start his professional career.

Morikawa debuted with an impressive tied 14th finish at the Canadian Open on June 9 last year and was rewarded with a world ranking of 1,039. Winner Rory McIlroy was then number three.

Two top-five finishes and victory in only his sixth PGA Tour start, at the Barracuda Championship, propelled Morikawa rapidly into the top 100 on July 28.

The only way is up: Collin Morikawa on his way to winning the 2020 US PGA Championship
The only way is up: Collin Morikawa on his way to winning the 2020 US PGA Championship GETTY IMAGES NORTH AMERICA / TOM PENNINGTON

By March this year he broke the top 50, courtesy of tied ninth at the Arnold Palmer Invitational, the last event before the coronavirus shutdown.

He flew back out of the traps in June and into the top 30 after losing a playoff to Daniel Berger at the Charles Schwab Championship, the first tournament after golf's restart.

His second victory at the Workday Charity Open on July 12 got him to 13th. "We got number one (win) out of the way, we got number two. Let the gates just open and let's keep going," he said.

That he did, the win at Harding Park taking Morikawa to a career-high world number five. And in a little over a year that gap to McIlroy has shrunk from 1,036 world ranking places to two.

While the world's eyes were on Morikawa's US PGA Championship win, another 23-year-old was suffering a brutal meltdown.

Former number one Lydia Ko threw away a five-shot lead with six to play as she chased a first LPGA Tour victory in more than two years at the Marathon Classic.

Ko began to wobble with a bogey at 14 and another at 16, but still held a one-stroke lead over the previous week's winner Danielle Kang as they stood on the tee of the par-five 18th.

Lydia Ko can't hide her agony after missing the putt to force a playoff at the Marathon LPGA Classic
Lydia Ko can't hide her agony after missing the putt to force a playoff at the Marathon LPGA Classic GETTY IMAGES NORTH AMERICA / Gregory Shamus

Ko collapsed.

Her second shot flew the green onto a cart path, her third careered back through into more rough and her fourth was duffed into a bunker.

She splashed out to 10 feet but missed the putt that would have forced a playoff, a double-bogey seven ensuring her 833-day win drought continued.

"It's tough," Ko said after her round, adding the 18th was "God's way of telling me it wasn't my day".

Brooks Koepka's straight talking has reignited his spat with Rory McIlroy.

The four-time major winner, who last year claimed he didn't see McIlroy as a rival because "he hasn't won a major since I've been on tour", this time took aim at third-round leader Dustin Johnson, who was two clear of Koepka going into Sunday.

"I like my chances," Koepka said of winning a third PGA in a row if it boiled down to a final-round duel, chiding that "DJ's only won one (major)".

Rory McIlroy fired back. "I certainly try to respect everyone out here," said the Northern Irishman, who has four majors of his own.

No love lost: Four-time major winners Brooks Koepka (left) and Rory McIlroy
No love lost: Four-time major winners Brooks Koepka (left) and Rory McIlroy GETTY IMAGES NORTH AMERICA / SAM GREENWOOD

"If he's trying to play mind games, he's trying to do it to the wrong person. I don't think DJ really gives much of a concern about that.

"I mean, it's sort of hard to knock a guy that's got 21 wins on the PGA Tour, which is three times what Brooks has." Ouch.

For the record, Johnson finished in a share of second while Koepka was four-over by the turn and slumped to tied 29th.

Newly crowned US PGA Champion Collin Morikawa has moved into the top five in the latest golf rankings released after his win at Harding Park:

1. Jon Rahm (ESP) 8.78 (+1)

2. Justin Thomas (USA) 8.77 (-1)

3. Rory McIlroy (NIR) 8.16

4. Dustin Johnson (USA) 7.75 (+1)

5. Collin Morikawa (USA) 7.51 (+7)

6. Webb Simpson (USA) 6.83 (-2)

7. Brooks Koepka (USA) 6.49 (-1)

8. Bryson DeChambeau (USA) 6.29 (-1)

9. Patrick Reed (USA) 5.97 (-1)

10. Adam Scott (AUS) 5.61 (-1)

11. Xander Schauffele (USA) 5.55

12. Patrick Cantlay (USA) 5.36 (-2)

13. Tommy Fleetwood (ENG) 4.83

14. Tony Finau (USA) 4.70 (+3)

15. Tyrrell Hatton (ENG) 4.61 (-1)

16. Tiger Woods (USA) 4.55 (-1)

17. Justin Rose (ENG) 4.49 (-1)

18. Daniel Berger (USA) 4.35 (+2)

19. Paul Casey (ENG) 4.31 (+9)

20. Matthew Fitzpatrick (ENG) 4.28 (-2)