Australia have completely dominated the series to take a 4-0 lead and only fitness and a tactical decision to bring in bowling all-rounder James Faulkner to exploit a green-tinged SCG wicket were likely to lead to changes in the team.
All-rounder Watson was the biggest concern after a groin strain restricted his bowling in the fourth Test in Melbourne but he and paceman Harris, whose right knee is a perennial concern, looked to be holding nothing back on Thursday.
Clarke, who is no longer a selector, said he thought spin-bowling would still play its traditional role in the last couple of days of the Sydney Test and said there would be no sentiment in the decision over whether to retain the same team.
"I think it would be extremely romantic but I think you've got to pick the best 11 players to help you have success in the conditions you're playing," he said.
"If conditions turn out to be similar to what they have been in the past four Test matches then I think the selectors will go that way but I think we certainly need to pick our best team to win this Test match.
"I don't have any idea of the team at this stage, I think we're waiting to see how the guys pull up tomorrow morning.
"But everybody's out in the nets batting and bowling so look I'm really confident guys will pull up fit but we need to give them every chance and see how they wake up in the morning."
Clarke endured four Ashes defeats and, before this series, his only taste of success was the 2006-7 series in Australia which ended up as a 5-0 sweep to the hosts.
The 32-year-old said he would have no need to talk to his team mates, none of whom had tasted Ashes success before this series, about the importance of repeating the feat.
"I think that desire burns within every single player in the changing room," he said.
"I said that before Melbourne and I think we showed with the way we played at the MCG and this Test is no different, it's just as important.
"We want to continue to run with the momentum we have at the moment and continue playing good cricket and getting the results we've been getting."