Coach Tom Willmott described Sinclair's performance as "the biggest, best and most consistent halfpipe riding of her life".
"Bex has proven her ability to peak at pinnacle events with a fourth place finish at the world championships last year, and now this result in a strong field," Willmott said.
"I am very happy with how everything came together for Bex this week, and look forward to getting stuck into further training in the springtime to help Bex achieve the artillery she needs to get on the podium in 2013 and 2014."
Sinclair stuck to the same formula as earlier rounds, landing a great run in the first of three, including a frontside 720 to Haakon flip combo before "stepping things up to push for the podium", Willmott said.
On her third and final run, she was unable to pull off her last-hit 900 to improve her score from run one.
Sinclair said she was "super happy" with her riding.
"I'm really stoked to have landed some personal best runs in competition and to end up fourth. I'm looking forward to my next event - the US Open in March."
Kelly Clark, of the United States, won the event - her 14th consecutive title, followed closely by Queralt Castellet, of Spain, who landed back-to-back 900s and a 1080 for silver.
Gretchen Bleiler, also from the United States, finished third.
Shelly Gotlieb competes in the slopestyle finals in the last day of competition tomorrow.
