The Real Madrid forward collected a lofted pass from Lucas Paquetá and calmly slotted past Placide to make it 3-0.
Haiti recorded their first attempt on target in the 48th minute after Danilo lost possession.
Sunderland attacker Wilson Isidor, a half-time substitute, hit a routine shot straight at Alisson.
Alisson later prevented Haiti from scoring their first World Cup goal since 1974.
The Liverpool goalkeeper made a point-blank save to deny a goalbound header from Ricardo Adé following a corner.
Jean-Kévin Duverne missed a chance for Haiti by poking his effort wide.
At the other end, Brazilian substitute Gabriel Martinelli saw his shot tipped onto the crossbar by an alert Placide.
Brazil continued to push forward but could not alter the scoreline.
Douglas Santos fired over the bar, Endrick had a goal ruled out for offside, and Ederson missed the target from a promising position.
Isidor forced another quality save from Alisson late in the match.
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Dominique Simon also attempted a long-range strike in stoppage time, but Alisson protected the clean sheet as Haiti became the first team eliminated from the tournament.
