Three players were sent off as Corinthians slumped to a controversial 1-0 defeat at third tier Luverdense and Everton Ribeiro scored a stunning goal to help Cruzeiro beat Flamengo 2-1 in Wednesday's eighth-final first leg games.
Santos youth player Gabriel said that he only went to Vila Belmiro to watch the Gremio match with his father, having trained earlier in the day with the youth team.
"I was playing a video game at home and came to watch the game with my father and only knew I would play when I got here," he told reporters. "It was a present."
He was included in the squad after a team mate was withdrawn because he had used a decongestant and officials feared he could fail a doping test.
After coming on midway through the second half, Gabriel, playing his seventh professional match, swept home Montillo's low cross in the 82nd minute. He completed his evening by receiving a yellow card for a shirtless goal celebration.
Corinthians were reduced to 10 men when Romarinho was sent off for a second bookable offence in the 72nd minute.
Tempers flared shortly afterwards and Corinthians substitute Emerson Sheik was dismissed along with Luverdense's Ze Roberto following a scuffle.
Luverdense snatched a shock win in the 90th minute when Misael slipped the ball past goalkeeper Cassio after appearing to control it with his arm.
Former AC Milan forward Alexandro Pato gave another lacklustre display for Corinthians and was jeered when he was substituted early in the second half.
Willian gave Cruzeiro a half-time lead against Flamengo before Everton Ribeiro produced his masterpiece in the 51st minute.
Running on to a chipped pass over the defence, he flicked the ball over a defender and smashed it into the top corner without letting it hit the ground.
Fluminense won 1-0 at Goias, helped by a penalty save from goalkeeper Diego Cavalieri, and titleholders Palmeiras, now in the second division, beat Atletico Paranaense by the same score.