Running with a time of 2:20:29, Mr Threlfall placed 35th in the men’s race and 39th overall, with over 52,000 runners finishing the marathon this year.
He ranked as the second-best Australian runner, just behind Matthew Fox, who lives in Chicago.
“I’m not sure if I can still claim first Australian. Surely, he has some kind of advantage living there,” Mr Threlfall said with a laugh.
Towards the end of the marathon, Mr Threlfall was racing in tow of the leading elite female runners, keeping pace with a runner in fifth place for around 4km.
He then caught up with a runner in fourth place who had won the London and New York marathons in previous years.
“I spun the head at one stage and said: ‘Come with me, we’re going to catch that girl up there.’ I’m not sure if she understood a word I said, but she burned me in the last 100 metres,” Mr Threlfall said.
“It was cool to get a front-row seat of the elite women’s race. The money those girls are running for, the difference between fourth or fifth could be 20 or 30 grand for that lady.”
While happy with his result, Mr Threlfall, whose personal best is 2:19:40, said poor sleep leading into the marathon and underestimating the toll of travel impacted his race.
“I felt like I was at 95 per cent, and my result was kind of what represented 95 per cent on the day,” he said.
“You’ve got small margins. When you’re five per cent off, that could all of a sudden be two seconds a kilometre. Times that by 42km, and that’s the difference between 2:18 and 2:20.”
Mr Threlfall said he planned to rest and recover in the month following the Chicago Marathon, held on October 13, but was eyeing races in Australia and Japan.
This year’s marathon saw the women’s world record broken by Ruth Chepngetich, and the second-fastest men’s time ever recorded on the course by John Korir.