Leishman, the defending champion this week, arrived at Aronimink Country Club 22nd in the standings and needing to remain in the top 30 to book a berth at East Lake.
After a disastrous opening 74 the Victorian looked in danger of giving up his spot but has fought back with consecutive rounds of 66 to claw back to 29th position.
With forecast bad weather threatening to shorten the tournament to 54 holes that would be enough to qualify though even if play goes ahead Leishman will fancy his chances.
He will likely be one of three Australians to make the season ending event with Jason Day and Cameron Smith guaranteed to advance while Adam Scott’s season will end this week.
The 2013 Masters champion needed to finish sixth or better this week but at just 2-under and T58 he is 12 shots behind current sixth place holder Keegan Bradley and has no realistic chance.
While the Australians have endured mixed fortunes for the week it is a tight tussle at the top of the leaderboard where low scoring has been the order of the day.
Heavy overnight rains left the Gil Hanse renovated course vulnerable on Saturday and the world’s best took advantage with 15 players shooting 5-under 65 or better.
Justin Rose leads alone at 17-under after a 64, one ahead of overnight leader Xander Shcauffele and a charging Rory McIlroy.
Schauffele made a disappointing bogey at the last to give up a share of the lead while McIlroy holed a long putt at the same green two groups prior to shoot 63.
Tommy Fleetwood and Rickie Fowler share fourth at 15-under with Keegan Bradley alone in sixth place at 14-under.
Tiger Woods endured another frustrating day on the greens and despite signing for a creditable 4-under 66 moved up only one place in the standings to T11.
He begins the final round five shots off the pace though if he can find some form with the putter is not out of the reckoning assuming play goes ahead.
An emphatic finish for @McIlroyRory.September 8, 2018
Because of the poor forecast play will again be in groups of three off both tees and starting early in the day which will see McIlroy paired with Rose and Schauffele in the final match.
With a 62 and a 63 already on his scorecard this week the four-time major winner looks dangerous and a head to head battle between he and the in-form Rose looks a possibility.
An upbeat McIlroy said after his round he felt the soft conditions played into the hands of the field and expected more of the same should play continue tomorrow.
“I hit more fairways again today and I putted better,” he said of his round.
“I lost three strokes on the greens yesterday. I missed a couple of short ones and today I holed the putts that I needed to and I hit more fairways and gave myself more opportunities.
“It was a weird day. They put a couple of the tees up the conditions were…obviously it was very wet and if you didn’t shoot 65 you were losing ground.”
Day is the best of the Australians at 11-under and T15, his 2-under 68 less than he would have liked.
The Queenslander is yet to find his best form in the play-offs though a 64 yesterday suggests he may not be far away.
Leishman is next best at T50, Scott is T58 while Cameron Smith, who played brilliantly the first two weeks, has faltered in Philadelphia to be near the tail of the field at even par and 65th in the 69 man field.
RULES - BALL MOVED BY WIND:
Want video tips delivered straight to your inbox? Subscribe to iseekgolf.com newsletters.