He looked behind him and realised his hopes of winning the US PGA Championship had suddenly, startlingly vanished.

Collin Morikawa's on-a-rope drive had stopped seven feet away from the hole on the 16th green.

It set up an eagle that dropped the Englishman two shots behind with two holes to play on Sunday.

What had been a jammed leaderboard turned into Morikawa's tournament to lose.

He didn't, and Casey had nothing to do but tip his cap.

"What a shot," Casey said when asked what went through his mind when he saw Morikawa's ball come to rest.

The 43-year-old Casey shot a four-under 66 to finish at 11 under, tied for second with Dustin Johnson and two behind the champion.

Casey is now none from 64 in majors – the longest current drought out there.

But this was not, in his mind, a day to focus on that.

“Watching Collin come down ... what a shot he hit on 16, he deserves it.” – Paul Casey

"I played wonderful golf, simple as that," Casey, who also has a third at the Open Championship and a fourth at the Masters on his resume, said.

"And watching Collin come down ... and what a shot he hit on 16, he deserves it."

Casey could have become the first Englishman since Jim Barnes in 1919 to win the US PGA.

He could have become the third oldest player to win his first major, trailing only Jerry Barber at 45 (1961 PGA) and Robert de Vicenzo at 44 (1967 Open Championship).

Instead, he is a runner-up for the first time.

More than that, he's happy to be finding his form as golf heads into a very busy stretch – with the PGA Tour playoffs, the US Open and the Masters all coming over the next three months.

"I do think I'm in a sweet spot," Casey said.

"It's taken me 43 years to get there, but yeah, pretty chilled out.

"I know what I'm capable of and I'm enjoying my golf."

- Eddie Pells, Associated Press