Mitchelton-Scott's South African ace trails overall leader Richie Porte by three seconds heading into stage five, knowing the 151.5km course from Glenelg to Victor Harbor represents his best chance to take the ochre jersey.

Porte (Trek-Segafredo) is the hot favourite to win the sixth and final stage - the signature route that finishes with the famed climb up Willunga Hill.

"We will go for everything we can," Impey said.

"We know it's going to be hard to beat Richie on Sunday.

"We will need a buffer to try to win the race overall, so any chance we can get, we are going to go for it."

Impey managed to slash Porte's lead in half on stage four, claiming three bonus seconds in the intermediate sprints, but could have done more damage.

"Unfortunately we didn't walk away with six seconds, we only got three," Impey said.

"But Trek have Mads (Pedersen) sprinting and (Jasper) Philipsen is also going for the sprint jersey so it makes it quite complicated.

"We will keep going for it, our tactics don't change. We will give it all until Sunday and what will be, will be."

Porte is chasing a second overall Tour win after saluting in 2017.

He has finished runner-up to Impey for the past two years, and four times overall.

"Daryl's a guy that can do everything and he can mix it with pure sprinters," Porte said.

"He's not the kind of guy that you want three seconds behind you, but we'll get through tomorrow."

Porte's teammates Kiel Reijnen, Koen De Kort and world champion Mads Pedersen will be important in his quest to retain the ochre jersey.

"They're a super team. You can't win races like this without committed teammates like that and the guy in the world champion's jersey putting you in the right position," Porte said.

"You've got to appreciate that."

Australian Associated Press