The halfpipe qualifiers were contested by 84 athletes, and just 18 men and nine women have made it to today's semifinals at Cardrona Alpine Ski Resort.
The top three men's and women's qualifiers go straight through to the finals, while the remainder of the semifinalists compete for the remaining spots.
The competition in Cardrona's 22-foot (6.7m) halfpipe was tough yesterday, with young Japanese rider Taku Hiraoka (14) achieving the second-highest scoring run seen in New Zealand.
United States snowboard superstar Shaun White scored the most points in New Zealand (47.1) when he won the halfpipe at the NZ Winter Games at Cardrona last year.
Hiraoka scored 43.8 points by attaining height and landing five well-executed tricks.
Junior world slopestyle champion Stale Sandbech (17), of Norway, was the second-highest scoring qualifier, making two consistent runs for 41.7 points.
Another young Japanese rider, Masakaze Yoshida (15), qualified third with 41.3.
In the women's event, Cilka Sadar (18), ranked 28th in the world, took a clear lead with 41.7 points.
Japan's Rana Okada (19) was second and Kelly Marren (US) third.
FIS head judge Ola Sundequist said today's finals promised a "very exciting" event.
"The best of each heat today were of a very high standard and they will be saving their best tricks for tomorrow's finals."
Sinclair qualified despite ongoing problems with a pre-season ankle injury, which prompted her withdrawal from the snowboard cross on Sunday.
Wanaka skier Mikey Austin (16) has also joined New Zealand's injury list.
A ripped calf muscle prevented her from competing in the freestyle slopestyle on Monday but she hopes physiotherapy may help her to compete in the skier cross on Saturday and the freestyle halfpipe on Sunday.
The semifinals are scheduled to start at 9.35am today, and the finals at 11am.
The championships continue tomorrow at the Snow Park with the parallel slalom.
