The New Zealand women's rugby sevens team have retained their World Cup title with a commanding 29-0 win over France in San Francisco.

Michaela Blyde ran in a hat-trick of tries, with Portia Woodman and Tyla Nathan-Wong also scoring as the Black Ferns Sevens proved too strong and too fast for the French.

Photo: Photosport

The New Zealanders' superior pace and unwavering defence proved the difference, Blyde's hat-trick in the final taking her tally to a tournament high of nine tries.

While two of her tries today were scored through her trademark pace, the first was all about grit and determination as she refused to die with the ball and powered through a number of French defenders to score.

Woodman scored shortly after following a great breakout from captain Sarah Goss before Tyla Nathan-Wong caught the French defence napping to extend the Black Ferns Sevens lead at half-time to 15-0.

France had plenty of ball in the second half but couldn't break through a New Zealand defensive line that refused to yield.

Sarah Goss said the match had been defined by her team's ability to control possession.

"It was about holding the ball, when they've got the ball they're hard to stop, they're strong runners, and they've got speed on the outside. So we knew if we could hold on to the pill we were going to convert points. When you've got players like Portia Woodman and Michaela Blyde on the outside they're hard to stop as well," said Goss.

Earlier, the Black Ferns Sevens had to work right to the final whistle to edge the United States 26-21 in the semi-finals, trailing the hosts 14-12 at half-time.

The break proved crucial for New Zealand, with replacement Gayle Broughton running 80 metres to score just after the restart before Woodman outran the US defence from the left wing to extend the lead further.

A try to Lauren Doyle on full-time wasn't enough to pull the match back for the US.

The New Zealand men's team are on track to defend their title, through to their semi-finals following their 12-7 win over France.

Despite receiving three yellow cards, the All Blacks Sevens emerged victorious and will now face Fiji in Monday morning's semi-final, after they thumped Argentina 43-7 in their quarter-final.

South Africa recorded a comfortable 36-5 win over Scotland to progress through to the other semi, where they will meet England, who edged the United States 24-19 thanks to an extra time try from Phil Burgess.

Photo: © Photosport Ltd 2018 www.photosport.nz

-RNZ