Leishman finished in 3rd place behind eventual winner Justin Thomas at the Dell Technologies Championship at TPC Boston, after building a two-shot lead through nine holes of today’s final round.
Jordan Spieth split the pair in second position and retained his lead in the FedEx Cup points race over Thomas in second position, while Leishman has improved to 7th and is now assured of a place in the Tour Championship in Atlanta in three weeks’ time.
Leishman shared the lead with reigning PGA champion Thomas heading into the final round, the pair one ahead of Paul Casey and two ahead of Spieth and blitzed the front nine.
The 33-year-old birdied four of his first five holes and added two more birdies by the turn to led by two over his playing partner Thomas - who had eagled the driveable par-four 4th in an outward nine of 32 - and Spieth.
Playing in the group ahead, Spieth too had reeled of a stunning first nine of 30, his highlight coming at the par-five 2nd where his approach from well over 200 yards finished 6 feet from the hole.
Things would change dramatically over the final nine holes however as first Leishman, then Spieth, began to falter, Leishman with bogeys at his opening three holes of the homeward nine to allow Spieth to take the lead through 13 holes but soon Spieth would open to door for Thomas.
Thomas birdied the 13th and 15th to move two ahead and with Spieth and Leishman continuing to struggle, Thomas eventually won by three over Spieth and by four over Leishman.
Leishman still had an opportunity to pinch the runner-up position on his own with a birdie at the last but his tee shot found the rough alongside the fairway bunker and from a grassy lie he found the hazard just short of the green.
He was able to get a club on his 3rd shot but had a restricted backswing and shanked the pitch to the right of the green and from an awkward lie was unable to get up and down and finished with a costly bogey.
It was however Leishman’s second best finish of the year behind his win at the Arnold Palmer Invitational but it was a case of what might have been, especially having controlled the tournament through nine holes.
Leishman will move to 23rd in the world rankings as a result of his impressive week when the rankings are revised in the next few hours which will be his highest ever ranking.
While they, along with his FedEx Cup standing, are significant milestones it will hardly make up for what was a gut-wrenching final nine holes today.
"Everything by the looks of it," said Leishman when asked what happend on the back nine. "You know, it was obviously a disappointing back nine for me. You know, got things going just the way I wanted to on the front and then a bad tee shot on 10. There was some tough holes out there but certainly not ten shots tougher than the front nine.
"Yeah, it's disappointing. But you know, with everything that's going on in the world, I mean, there's certainly worse things going on. You know, you have to put things into perspective. Obviously very disappointed. But we're good to go.
"The game is in a good spot, playing well. Putter feels good, which is very important in match play. Looking forward to getting up to Chicago and hopefully climbing up a little higher up the FedExCup standings, and then anything can happen in THE TOUR Championship."
For Thomas, it's his 5th win of a stunning season with the opportunity for two more at the BMW Championship in Chicago in two weeks’ time and at the Tour Championship in Atlanta beginning on September 21st.
Jason Day continued his strong recovery from his opening round of 75, today adding a round of 66 to finish 25th this week and in 28th position in the FedEx Cup points list he is well placed to advance to the Tour Championship provided he puts together a reasonable week in Chicago.
The only other Australian to advance to the BMW Championship is Cameron Smith who missed the cut this week.