South Africa celebrate winning the Cup final against Fiji on day two of the IRB Rugby Sevens at Westpac Stadium in Wellington on January 29, 2017

World Rugby Sevens Series leaders South Africa and two-time defending series champion Fiji welcome back top players for the USA Sevens tournament that begins Friday at Las Vegas.

The Blitzboks top the table with 85 points after wins in Wellington and Sydney plus the season-opener at Dubai but lost the Cape Town final to England, who are second on 68, four points ahead of Fiji in third.

After a 36-hour trek from South Africa to Nevada by way of London, Blitzboks coach Neil Powell was pleased with his lineup's fitness as training resumed for Vegas and next week's sixth leg in Vancouver, Canada.

"I am happy where we are with our preparations and will take it slow at the beginning," Powell said. "The turn-around between the tournaments is quite short and the guys do pick up bumps and bruises, but I am happy with the squad's fitness. There is still one or two things we need to work on, but I am happy that we have enough time to sort out those small margins."

South Africa welcomes back flyer Werner Kok, the 2015 World Rugby Sevens Player of the Year, and playmaker Cecil Afrika. Kok, who helped South Africa to a 2014 Vegas title, was hurt for last year's Vegas trip and missed most of the Sydney victory run last month with a calf strain.

"It is never nice to miss out on a tournament, but luckily that niggle is sorted out and I am feeling fresh and ready to go," Kok said. "Now we need to get onto the field and I am looking forward to that... I have very good memories."

Afrika, South Africa's top scorer with 1,167 points over 47 tournaments and the 2011 World Sevens Player of the Year, is back at full fitness after missing the trans-Tasman twin titles.

"It is great to be back with the guys," Afrika said. "What struck me immediately was how trusted our structures are. I slotted in immediately.

"I am happy to be fit again and want to go out there, have fun and do my part for the team."

- Fiji adds Olympians -

South Africa, seeking a first overall crown since 2009, will face Wales, France and Canada in Pool A.

Pool B features England, Samoa, Chile and the US hosts while Pool C has New Zealand, Argentina, Russia and Kenya and Pool D contains Fiji, Australia, Japan and Scotland.

Fiji were the USA Sevens champions in 2015 and 2016

Fiji, the USA Sevens champions in 2015 and 2016 on the way to the overall series crowns, made three changes from the Wellington-Sydney lineup for the North American events, adding 2016 Rio Olympic gold medalists Masivesi Dakuwaqa and Apisai Domolailai and former national sevens winger Waisea Nacuqu.

"Selection for these two legs have been very competitive and I am pleased with the work that the players have put in over the last two weeks," Fiji Sevens coach Gareth Baber said. "Masivesi and Apisai come in and I am looking forward to seeing their leadership and points of difference on display over the next two legs. Also a return for Waisea, who has been very impressive during our training sessions."

- England squad unchanged -

England offer an unchanged lineup from the Sydney runner-up squad.

"Having this level of consistency is a big plus for us," England Sevens coach Simon Amor said. "When you combine this with experience right across the squad, it becomes a genuine 12-man effort. This allows us to manage game time and load more effectively and the benefit showed in Sydney through the impact that every player made."

The USA Eagles will be without speedy Carlin Isles, who will miss the remainder of the series as he undergoes knee surgery.