The race for World Cup spots is heating up, but Australian skipper Michael Clarke hopes the guessing games will soon be over.

Australia are set to experiment with several players during the five-match one-day series against South Africa, with selectors keen to suss out what combinations will be best suited for the World Cup.

All-rounder Nathan Coulter-Nile has been given an early chance to impress, while a fit-again Shane Watson also has plenty to prove during the series.

In-form batsman Steve Smith was a surprise omission for Friday’s series opener against South Africa at the WACA, but the 25-year-old still has a good chance to earn a World Cup berth.

Clarke is no longer a selector after resigning from the position in the wake of Mickey Arthur’s axing as coach in 2013.

Head coach Darren Lehmann, Rod Marsh, Mark Waugh and Trevor Hohns are now in charge of team selection, and Clarke hopes any experimenting will be finished once the current one-day series concludes.

“We’ve got this series to give guys an opportunity if the selectors are still not certain on their 15,” Clarke said.

“I’d love to see the squad that’s selected for tri-series (against India and England) … be our one day World Cup squad of 15 players.

“I’ve voiced my opinion to Rod and to Darren in regards to that.

“That way we can spend that time together in preparation for the World Cup.”

However, he said the selectors were probably still considering a couple of positions.

“It’s always tough because there’s still so much cricket to play leading into the World Cup.”

Watson, who has battled ankle and calf problems in recent months, returns to the one-day fold for the first time since January.

Clarke said the 33-year-old remained a key cog to the team.

“I have said for a long time that if he batting and bowling, he is in any team,” Clarke said.

“If he can stay fit and healthy, that helps us a lot in all three formats of the game.

“He’s a senior member of the team, so his leadership and experience is really important.”