Kelly Slater says he'll need to be near perfect if he's to resurrect his dwindling world title hopes and stay in the hunt for a record 12th surfing crown.
Slater is fourth in the world rankings at the halfway point of the tour with Australia's Mick Fanning leading the title race from compatriot Joel Parkinson and Hawaii's John John Florence.
The 40-year-old Slater remains in the hunt to defend his Hurley Pro title at Trestles in California which is event six of the 10 tournament world tour.
He will face Frenchman Jeremy Flores in a round five eliminator when action resumes at the Californian break.
Parkinson and Florence kept the pressure on Slater by moving directly into the quarter-finals with round four wins, while Fanning is up against fellow Aussie Julian Wilson in heat one of round five.
Floridian Slater knows that after a patchy year, where he had a rare 13th-place finish and a missed event, there is no room for error in the tournament.
"My back is against the wall, to be honest," said Slater on Wednesday.
"Every heat is really important if I want to be in the title race at the end of the year.
"I don't really have any room to move after missing Brazil and just a stupid mistake in Tahiti where Ricardo (dos Santos) got me - those are my two throwaways for the year, but sometimes that's good, it helps you keep your focus.
"I've just got to make the right choices and hope I don't get smashed by someone early on."
Slater has made seven finals in the event's 12-year history, and a victory at this year's Hurley Pro would mark his 50th ASP World Championship tour win.
Queenslander Parkinson is full of confidence ahead of the quarter-finals.
"That first real good hit was sweet ... it allowed me to feel confident from the first turn," Parkinson said.
"I just try and keep up with (Fanning).
"I saw his last performance and although it probably wasn't one of his best, it was really solid.
"He's a momentum builder ... towards the end of the event he starts to really find his form."