The 20-year-old from Glasgow, whose 2014 campaign was hindered by injury, duelled with rival Dorian Coninx for the title before the Frenchman delivered a decisive late break to win by 14 seconds.
It was a repeat of their 1-2 at junior level in London 12 months ago but, with plans to chase an Olympic berth next season, Austin believes it proves he has what it takes to reach the top.
“The bike wasn’t great, just easy and I couldn’t get anything going,” he said. “The run was good, I felt really good until about seven kilometres then my legs started to fall apart. Dorian kicked at 8k and I couldn’t follow. It’s been a tough year, though, and I’m happy to finally get a result. It’s a big step forward from earlier in the year and I think there’s a lot more to come over the Olympic distance.”
Great Britain team-mate Gordon Benson came third, with Austin’s fellow Scot Grant Sheldon in 16th.
Commonwealth champion Jodie Stimpson ended fourth in the world championship standings after the Englishwoman could finish only 13th in the women’s Grand Final as the US’s Gwen Jorgensen clinched the title with victory.
“I haven’t felt good in the water since Stockholm,” Stimpson said. “If you’re not feeling 110 per cent in this field you’re going to get spat out of the back. I was hoping I’d make that front pack and then I’d have a shot but I couldn’t.”
Jorgensen, meanwhile, became the first American champion in a decade. The 28-year-old, who led the overall standings entering the final race, broke clear of her rivals in the closing ten-kilometre run to post a winning time of two hours five seconds. New Zealand’s Andrea Hewitt finished the race second in 2:00:21 with her compatriot Nicky Samuels third in 2:00:31.
“I don’t think it’s sunk in yet, that I’m world champion,” Jorgensen said after becoming the first woman to win five World Triathlon Series events in a single season. “This race was interesting because, going in, I knew I only had to get top 16 to be world champion. I really wanted to win it on this day and it’s been the sole focus all year.”
Jorgensen’s world title was the first for the US since 2004, when it was won by four-time Olympian Sheila Taormina.
American Sarah Groff, who finished Saturday’s event fourth in 2:01:20, ended the season second in the overall standings and secured the world championship silver medal.