Diego Godin's late goal gave Uruguay a 1-0 win over 10-man Italy and booked their place in the round of 16 -- but the match was overshadowed by an incident in which Luis Suarez appeared to bite Giorgio Chiellini.
Suarez, who served lengthy bans for biting opponents while playing for both Ajax and Liverpool, clashed with Chiellini in the 79th minute.
Television replays showed Suarez moving his head towards Chiellini who responded by swinging an arm, before chasing the referee to apparently insist he had been bitten on his shoulder.
Suarez could face suspension if FIFA disciplinary officials uphold Chiellini's protests, and the incident cast a shadow over a hard-fought win for the South Americans.
Defender Godin rose highest to nudge home an 81st-minute corner to end the resistance of the Italians, who had played with 10 men since Claudio Marchisio's sending-off on the hour.
The dramatic ending came in stark contrast to an abysmal first period of a match the Uruguayans needed to win in order to progress along with Costa Rica.
Despite the onus being on them to attack, Oscar Tabarez's side barely managed to muster a single chance of note in a dismal first half which was largely controlled by the Italians.
In an opening spell constantly broken up by niggling fouls, Chiellini had an early penalty claim waved away and Andrea Pirlo saw a long-range free-kick pushed over the bar by Fernando Muslera.
Balotelli's raised foot challenge on Cristian Rodriguez earned him his costly yellow card but the extrovert former Manchester City man continued to provide what passed for the most persistent threat on the pitch.
Ciro Immobile should have put Italy ahead in the 28th minute when he met Mattia De Sciglio's low cross into the box from the left but fired over the bar from just inside the box.
Suarez, clearly struggling for match fitness, was largely anonymous for the opening half-hour but had his first chance in the 33rd minute when he nipped in behind the Italian defence and saw his shot from a tight angle flapped away by Buffon, who also saved the follow-up from Nicolas Lodeiro.
Uruguayan frustration was summed up toward the end of the first half when Martin Caceres attempted a ridiculous 70-yard chip over Buffon which sailed well wide.
As the second half got under way there were few signs of urgency on Uruguay's part, although Edinson Cavani demanded a penalty after falling theatrically in the box under the challenge of Leonardo Bonucci.
The South Americans gradually started to press and had their first real chance in the 58th minute when Rodriguez played a sharp one-two with Suarez, cutting into the box from the left but splaying his shot wide.
Moments later, the Italians were reduced to 10 men when Marchisio was sent off for a careless, chopping foul on Egidio Rios.
But despite the extra man advantage, Uruguay continued to struggle to create openings with the Italian defence adept at suffocating their opponents' attacking threat.
The golden opportunity the Uruguayans were hoping for arrived in the 65th minute when Cavani sent Suarez through but Buffon got down to his right superbly to palm away the Liverpool man's shot.
Controversy raged in the 79th minute after Chiellini and Suarez fell after an off-the-ball clash in the Italian box.
Both players fell to the floor with Suarez seeming to lose a tooth in the melee, which is likely to be the subject of further investigation.
Two minutes later the South Americans grabbed the goal they needed when Godin rose highest to send his side through to the knockout stages as group runners-up.