Cavani's sending off with 20 minutes to go capped a miserable night for his side, despite having the better of things for much of the first half.
Chilean referee Roberto Tobar showed him a yellow card after his lunge caught Richarlison on the ankle. But after a VAR check, that changed to red, leaving Cavani incredulous, and he left the pitch reluctantly.
Brazil almost drew first blood after two minutes of a lively opening, when Uruguay keeper Martin Campana parried a close range shot from Gabriel Jesus after the Manchester City striker bought a yard of space on the edge of the six-yard box.
Almost immediately, Uruguay's 21-year-old Benifica star, Darwin Nunez, turned Brazil full-back Danilo inside the area and rattled Ederson's bar after a neat pass from River Plate's Nico De La Cruz.
Uruguay fashioned another gilt-edged chance when Nathan Nandez's cross from the right was headed over by Cavani.
Brazil had most of the ball, but could find no way through a well-marshalled Uruguay midfield.
They finally broke through however with their first real chance in half an hour, and with a large slice of luck.
Feeding on a slick layoff from Gabriel Jesus, Arthur's shot from outside the area took a wicked deflection off the back of Uruguay defender Jose Gimenez, wrongfooting the luckless Campana, who could only watch it bounce into the net.
Two minutes later, a slick through ball from the Juventus forward put Liverpool's Roberto Firmino in on goal but his left foot shot lacked the power to beat Campana.
Brazil gradually got on top on midfield as the half wore on, and struck a body blow to Uruguay's hopes of a revival when Everton striker Richarlison headed in a long cross from Renan Lodi out on the left, to score his 8th goal for Brazil.
It was a cruel blow just before half time, emphasised when Uruguay skipper Diego Godin powered a header against the Brazil bar from a free kick by De La Cruz.
Showing slickness on the ball, Brazil began to cruise in the second half, even without the injured Neymar.
Uruguay missed the physical presence of Luis Suarez, out with a positive Covid-19 test, and Brazil center halves Thiago Silva and Marquinhos had the better of a sometimes tasty encounter with their former Paris Saint-Germain teammate Cavani.