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The pair, who both won bronze at the 2018 Olympics in Pyeongchang and have bounced back from a spell with Covid-19, shone at the Mammoth Mountain (California) round of the world cup at the weekend.
Porteous (20) again signalled he is the man to beat in freeski halfpipe by winning the title with a remarkable score of 97 out of 100.
After a bobble on his right double 1620 landing in run one had him sitting in eighth position, the pressure was on for run two.
Porteous was the only athlete who could upset the all-American podium at this point in the event.
"It was pretty tough," Porteous said.
"The last few competitions I haven’t skied at my best so the bobble in run one was a bit frustrating, to be honest.
"I spoke with my coach, Tommy, at the bottom and we decided it was all or nothing, so I should attempt that run again and just do my best."
This was the final freeski halfpipe world cup before Porteous heads to China for the Olympics.
"It gives me a lot of confidence going into Beijing. I was concerned that I wasn’t quite where I thought I was, so to get the win today is really epic”.
Porteous’ brother, Miguel (22), put down a solid performance to finish fifth.
Fellow Wanaka skier Ben Harrington (20) achieved a career-best result with sixth at his second world cup finals appearance, his first being just a week ago in Calgary.
Gustav Legnavsky (16) posted his own career-best result, finishing eighth in his first world cup final.
The teenager showed everyone why he belonged in the finals when he came out swinging in his first run with a switch left double 1080 and a huge left double 1260.
“I was really nervous at the top of my first run because not only was it my first run in my first finals, it was also a new and technical run I had never landed in competition before," Legnavsky said.
"Once I got to the bottom, I was relieved because I landed the run and I was stoked to have shown everyone what I can do."
Two-time Olympic champion David Wise (US) finished second and compatriot Aaron Blunck third.
Sadowski-Synnott (20) was "super stoked" to add another medal to her bulging collection with silver in the snowboard slopestyle.
She put down a solid first run with good variety on the rails and a smooth switch backside 900 on the first jump to take the lead with a score of 82.50.
Jamie Anderson (US) landed a strong second run to bump the Kiwi into second place.
Sadowski-Synnott knew she had to go all out on her second and final run.
She was lacing together a technical and stylish effort but came unstuck on the final jump, attempting a back 1080.
Queenstown boarder Tiarn Collins (22) claimed bronze in the men’s snowboard slopestyle.
It was a special moment for Collins as it had been nearly two years since he last stood on a world cup podium.
He came out of the start gate swinging, stitching together a solid run with clean, technical rails and a huge backside 1620 on the final jump to secure a score of 73.44.
Although he was unable to put together a clean second run, his strong first run score held up for third.
"I am really stoked. I just wanted to land that run as well as I could," Collins said.
It was the fourth world cup podium of his career and his third in slopestyle.