The women's 200 metres, 20 kilometre walk, triple jump and javelin will also be decided, along with the men's 110 metres hurdles, while American Bryan Clay begins the defence of his decathlon title.
American Wariner has been in dominant form throughout the heats, easing to victory in his semifinal in a time of 44.34 seconds.
He faces stiff competition from compatriots Angelo Taylor and Lashawn Merritt, along with Chris Brown of Bahamas, but is in the form to threaten Michael Johnson's eight-year-old world record of 43.18.
World record holder and Olympic champion Liu Xiang of China bids for the men's 110 metres hurdles title, with Americans Terrence Trammell and David Payne among his likely challengers on the day.
“I felt better today than I did on Wednesday because I didn't sleep a lot the night before and was more tired,” Liu said.
"Today I was more relaxed. Tomorrow is going to be a good opportunity for me." Clay, plagued by injuries since winning the decathlon title in Helsinki, should be pushed all the way by his resurgent compatriot Tom Pappas, the 2003 world champion, and Czech Roman Sebrle, the Olympic champion.