Driving rain throughout the final round made the air heavy and birdies hard to come by as Harman defended his five-shot lead with a mixture of clinical control and exceptional putting.

Carrying Australia’s hopes into the final day, a 10-foot birdie putt at the par-5 15th brought Day to within four of Harman in a share of second and with a sliver of hope, but it would be gone in an instant.

Two groups further back Harman drained a 40-footer at the 14th to push his lead back out to five, providing an additional exclamation point with a perfectly executed birdie on 15 to move six clear of the Australian.

Harman’s 1-under 70 and 13-under total clinched a six-stroke win, joining Shane Lowry’s 2019 victory at Royal Portrush as the equal largest margin of victory since Louis Oosthuizen’s seven-stroke win in 2010.

Seeking a second major championship to go with his 2015 US PGA win, Day’s 2-under 69 only reduced the deficit he began the day with by one.

After an early bogey on three, Day dragged himself back into championship contention with back-to-back birdies to close out the front nine.

He converted a birdie chance from just inside nine feet at the par-4 eighth and then – for the second day in succession – made birdie at the par-3 ninth despite missing the green with his tee shot.

Birdie opportunities from eight, 20, 20 and 35 feet would elude him from holes 11-14 before his 10-footer on 15 brought him one shot closer to the leader.

A superb tee shot at the short 17th would also go unrewarded, a two-putt for par at the 72nd hole wrapping up a tie for second, bettering his tie for fourth at the 2015 Open at St Andrews.

“Unfortunately I hadn’t played that great in the majors this year, so it was nice to be able to finish this major off and finish tied second,” said Day. “Just the slow, gradual increase in confidence through good play.

“I wish I would have cut into the lead a little bit more. You just never know. When someone has such a great lead, a big lead, big margin, and then you kind of cut into it, you just never know what they’re going to do under the pump.

“To have a six-shot lead going into the last hole, a lot of breathing room there.”

Cameron Smith’s defence ended with a round of 2-over 73 and a tie for 33rd, the 29-year-old left frustrated by an uncharacteristically difficult week with the putter yet determined to taste victory on the links again in future.

“I can’t wait to get back next year. Hopefully I can do a better job of being up there,” Smith said.

“At the start of the week I felt as though I was playing good enough golf. It just wasn’t my week.

“Usually I’m leaning on my putter to make good scores, and this week it was almost the opposite.”

Adam Scott produced his best score of the week – a 2-under 69 – on the final day to draw level with Smith at 1-over for the championship.

A holed bunker shot for eagle from one of Royal Liverpool’s treacherous pot bunkers at the par-4 fourth was a spectacular highlight for the 43-year-old, two closing birdies the best possible finish to his 23rd Open Championship.

“It’s a nice way to finish,” Scott offered.

“I did today what I needed to do the other days and I would have had a nice week, but I finished poorly every other round.

“Just kind of made up the numbers this weekend.

“It’s kind of the reason I still work hard at my game, thinking I could have a chance to get that other hand on the jug that I was so close to getting.

“That’s what I’ll be working at over the next 12 months, to come back and have another crack and be in good form and maybe steal a trophy later on in my career.”

At the other end of the career spectrum, Min Woo Lee added to his major championship bank of experience with a final round of 4-over 75 and tie for 41st.

Top 10 through 36 holes, the 24-year-old began Round 4 with bogeys at two of his first three holes and never really clawed them back.

“It was pretty brutal,” Lee surmised. “Didn’t really have the mindset that it was going to be that wet for that long.

“All day we pretty much had the umbrella up. Yeah, it wasn’t easy.”

Final scores
1             Brian Harman                    67-65-69-70—271 $US3m
T2           Jason Day                           72-67-69-69—277 $1,084,625
T33        Adam Scott                        72-73-71-69—285 $84,112
T33        Cameron Smith                 72-72-68-73—285 $84,112
T41        Min Woo Lee                    71-68-72-75—286 $58,725
T52        Ryan Fox (NZ)                    78-67-69-74—288 $43,433
MC         Lucas Herbert                    71-76—147
MC         Travis Smyth                      78-72—150
MC         Daniel Hillier (NZ)             78-73—151
MC         Haydn Barron                    74-77—151
MC         David Micheluzzi               77-75—152
MC         Connor McKinney             76-77—153
MC         Harrison Crowe (a)           76-80—156

Photo: Gregory Shamus/Getty Images