Brazil will play Mexico in Saturday's men's Olympic football final at Wembley after easing past South Korea with a 3-0 victory.
Romulo put Brazil ahead at Old Trafford with a first-time strike after a superbly weighted pass from Oscar.
Leandro Damiao struck twice after the break to become the tournament's leading scorer with six goals.
Brazil have now scored 15 goals in five games as they bid to win the tournament for the first time.
Mano Menezes's team are unbeaten and have found the net three times in every match they have played, justifying their pre-tournament billing as gold medal favourites.
South Korea, who beat Great Britain on penalties in their previous fixture, have the consolation of a bronze medal match against Japan in Cardiff on Friday.
And Hong Myung-bo's team can take encouragement from the start they made in front of 69,389 at Old Trafford, a crowd that included Fifa president Sepp Blatter and Manchester City boss Roberto Mancini.
South Korea dominated the early stages of the match, but could not convert any of the chances they created.
Sandro hooked the ball off his goal-line from Kim Hyun-sung's header and it took a desperate challenge from Juan Jesus to thwart Ji Dong-won, who looked poised to strike from six yards.
Ji then went close from long-range but goal-shy South Korea, who had found the net just three times in their previous four games, eventually paid for their failure to take the lead.
Lee Bumyoung, the penalty shootout hero against GB, denied Leandro, who also missed from a tight angle after the keeper had parried an effort from Sandro as Brazil finally started to find some rhythm.
Lee made a smothering save at the edge of his box and Kim Young-gwon cleared off his line after Alex Sandro, selected instead of Hulk in a change from the team that beat Honduras, had hooked the loose ball goalwards with the keeper stranded.
But when the Red Devils fatally backed off as Oscar ran at their defence, the new Chelsea signing had time to pick out Romulo charging down the right-hand side and the Vasco de Gama midfielder slotted home at the near post with a first-time effort.
Sunderland striker Ji, who scored against Great Britain but had an off-night against Brazil, shot over on the turn early in the second half and his side were unlucky not to be awarded a penalty when Tottenham's Sandro appeared to impede Kim Bo-kyung.
The tie was effectively over after 56 minutes when Leandro slotted home Neymar's cut-back after Marcelo just failed to reach the ball.
And Leandro moved ahead of Senegal's Moussa Konate as the tournament's top scorer when he dug the ball out from under his feet to shoot into the bottom corner from 14 yards shortly afterwards.