Cielo's task has possibly been made easier after both South African Roland Schoeman, champion in 2005 and 2007, and world record holder Rafael Munoz of Spain failed to make it through to the final.
Cielo was second quickest in the semi-finals behind compatriot Nicholas Santos, with French pair Frederick Bousquet and Florent Manaudou and Germany's Steffen Deibler lurking further back.
Ye, gold medallist at the London Olympics in the 200m and 400m individual medley, is aiming to follow in the footsteps of American Kathryn Hoff, who won at the 200m medley distance at the world championships in 2005 and 2007.
Ye was second fastest in Sunday's qualifying behind Katinka Hosszu of Hungary, with Australian Alicia Coutts, second behind Ye in London, third.
There are two more finals on Monday.
Dana Vollmer of United States is chasing another gold in the 100m butterfly after her triumph in London and Australia's Christian Sprenger looked in fine shape as he came through fastest in Sunday's qualifying for the men's 100m breaststroke.
Olympic champion and world record holder Cameron Van Der Burgh of South Africa, who is coming back from a knee injury, was equal-second quickest behind Sprenger with the same time as American Kevin Cordes.
(Reporting by Iain Rogers, editing by Toby Davis)
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