Australian George O'Brien has burst into contention in the State New Zealand Ocean Swim series, with an impressive victory in round three in Wellington today.

O'Brien, 22, fought off strong challenges from New Zealand's Nathan Capp and Dylan-Dunlop-Barrett, in a race which was shortened from 3.3km to 2km because of strong winds and choppy conditions.

After a strong start from O'Brien, the trio swam together from the 500m mark before O'Brien attacked near the end, sprinting up the beach at Oriental Bay to claim the victory.

"That wasn't an easy race," he said. "That wind and chop made it was really difficult to find a rhythm, but every point counts in this series, so I'm really happy to come away with the win."

Pushing O'Brien all the way was 2012 London Olympian Dylan Dunlop-Barrett, and Tauranga swimmer Nathan Capp, who last month broke Kane Radford's New Zealand 1500m freestyle record by more than five seconds.

"I'm always disappointed when I don't win," Capp said.

"But I can't be unhappy finishing second to someone like George, who just put in that attack at the end. I couldn't stay with him," he said.

It's the second time O'Brien has won this race. He was victorious in 2012, before missing last year after having shoulder surgery. He joins Kane Radford and another Australian, Jarrod Poort, as race winners in the series so far.

Each swimmer's leading three efforts count towards the series, with double points on offer at the final race in April, the State King of the Bays. Both Radford and Poort decided not to swim this round.

The women's race, meantime, was dominated by Wellington's Emma Robinson.

The 18-year-old, who won the 5km open water national title earlier this month, raced away at the start, and the expected head-to-head battle with the national 10km open-water champion Grace Somerville, who finished 5th, never eventuated.

"It's really cool to win my home race," Robinson said.

"Swimming against the wind and chop was challenging, but from the turn in when the conditions were behind us, I actually enjoyed it. I'm really pleased to get my first win as it puts me in contention for overall honours for the series."

Robinson joins Charlotte Webby and Paige Schendelaar-Kemp as winners so far. Both opted not to swim this round of the series.

Today's race in Wellington was held in windy and choppy conditions, forcing race director Scott Rice to make a late change to the course.

"With Met Service forecasting a strong northerly gusting up to 40 knots, we had to use our 2km contingency course today," he said.

"So while those hoping to swim 3.3km today didn't get to do it, the safety of the swimmers is paramount.

Race four in the six race series is the State Le Grande Swim in Akaroa on February 22nd. The final two races in the series are the State Sand to Surf in Mount Maunganui on March 22nd and the State King of the Bays on Auckland's North Shore on April 12th.

Results: 2013 Capital Classic

Men

1. George O'Brien (Queensland) 20:22
2. Nathan Capp (Tauranga) 20:25 +0:03
3. Dylan Dunlop-Barrett (New Plymouth) 20:27 +0:05
4. Phillip Ryan (Auckland) 20:50 +0:28
5. Liam Albery (Wellington) 21:01 +0:39

Women

1. Emma Robinson (Wellington) 22:38
2. Josie Kozyniak (Wellington) 22:55 +0:16
3. Courtney Carson (Lower Hutt) 22:56 +0:17
4. Nikki Chapman (Wellington) 24:18 +1:40
5. Grace Somerville (Ashburton) 24:31 +1:53

2013/2014 Series Standings

Men

1. Phillip Ryan * 296.85
2. Jarrod Poort 199.81
3. Dylan Dunlop-Barrett 199.60
4. Nathan Capp 199.54
5. Ben Ruback 189.93

Women

1. Emma Robinson 196.71
2. Paige Schendelaar-Kemp 196.61
3. Courtney Carson 196.17
4. Liana Smith 191.84
5. Grace Somerville 191.07