Michaela Blyde is congratulated by team-mate Gayle Broughton after scoring New Zealand's second try.

Kelly Brazier is not the quickest member of the New Zealand women's sevens team, but the hero of Sunday's extra-time thriller says her fitness got her across the line for the match-winning try.

The 28-year-old ran 80 metres to score after the final hooter of extra time as the Kiwis beat arch rivals Australia 17-12 in the gold medal match at the Commonwealth Games on a sweltering Sunday afternoon at Robina Stadium on the Gold Coast.

It was a monumental effort after a torrid 19 minutes of action in the heat of the afternoon, with her team-mates struggling to run down the field afterwards to go and celebrate with her.

GETTY IMAGES Portia Woodman skips out of Charlotte Caslick's attempted tackle.

She took a quick tap from a penalty in her own 22 after getting the go-ahead from captain Sarah Goss, beat a defender in midfield, ran to about halfway, looked for support, but didn't see any, so pinned her ears back and found the energy to get to the corner for the try.

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"I'm probably not the quickest, but I pride myself on my fitness. Obviously it was 19 minutes in so I had a bit of a look around and thought it's now or nothing, so just went for it," Brazier said after collecting her gold medal.

PHOTOSPORT Kelly Brazier crosses for the match-winning try.

"I had a few chasing but just thought I'm gonna go and it paid off in the end."

When she was looking around on about the halfway line, it appeared as though she might not have the legs to make it to the tryline.

But she said it was more a case of thinking linking up with support would be the better option.

DAN MULLAN/GETTY IMAGES Kelly Brazier left everything on the pitch as she stormed 80m to win the match in extra-time.

As she sprinted clear, coach Allan Bunting said he became just another spectator in the crowd.

"I was screaming and giving her a bit of a turbo boost with every step," he said with a laugh.

Once across the line, Brazier said her mind went clear.

"Nothing to be honest," she said about what was going through her head at that stage.

"All I could feel was my lungs going up and down in the air. I was just worried about trying to catch my breath back and then the girls just jumped on top of me so it made it a bit hard to breathe. So I was just trying to breathe, that was it."

It ended an epic final in which New Zealand had led 12-0 at halftime after tries to Portia Woodman and Michaela Blyde.

But a strong second-half fightback by Australia saw Emma Tonegato and Emilee Cherry crash over to make it 12-12 at fulltime, meaning sudden-death extra time.

A major moment in the match came just before Brazier took the quick tap when Australia's Vani Pelite looked for all money like she would score the winning try in the final minute, only for a gut-busting efforts from Goss and Niall Williams stopped her within 10 metres of the line.

"Niall chased back 50, 60 metres and caught them five metres out from the line and that to me was the changing moment of the game," Brazier said.

"Our team prides itself on defence. If you don't defend you can't turn the ball over and attack."

It was then left to Brazier to be the hero.

Earlier in the semifinals, New Zealand beat England 26-5, while Australia had eased past Canada 33-7.

AT A GLANCE

Final

New Zealand 17 (Portia Woodman, Michaela Blyde, Kelly Brazier tries; Tennika Willison con) Australia 12 (Emilee Cherry, Ellia Green tries; Emma Sykes con) after extra time. HT: 12-0. FT: 12-12

Semifinal

New Zealand 26 (Sarah Goss, Michaela Blyde, Shakira Baker, Portia Woodman tries; Tyla Nathan-Wong 3 con) England 5 (Abigail Brown try). HT: 12-5.