Both goalscorers were sent off in a 1-1 draw between Santos and Corinthians, Cruzeiro went top with a 2-1 win over Criciuma and Ronaldinho scored from a free kick as South American champions Atletico Mineiro held Botafogo 2-2.
Flamengo went ahead midway through the second half of Wednesday night's match when full-back Joao Paulo converted a penalty and it got worse for Portuguesa, 19th in the 20-team table, when Fernandinho was sent off with four minutes left.
Flamengo failed to make their advantage count, though, and Portuguesa had a last throw of the dice when they won a corner two minutes into stoppage time.
Lauro went forward to join the attack and out-jumped several defenders to score with a downward header from near the penalty spot, helped by a blunder from Leo Moura who should have cleared off the line.
"I can't explain it, when I was warming up I remembered another goal I scored against Flamengo 10 years ago" Lauro, who was playing for Ponte Preta on the previous occasion, told reporters.
Santos, still smarting from an 8-0 friendly defeat at the hands of Barcelona on Friday, fell behind after only three minutes when Paulo Andre headed in following a corner.
But they regained their composure and Willian Jose levelled early in the second half.
Oddly, Paulo Andre and Willian Jose were both sent off in the 67th minute after they got involved in an argument involving two other players.
Botafogo lost the championship lead when they conceded a stoppage time equaliser in a 2-2 draw with Atletico Mineiro, who picked up their first point in four games since they won the Libertadores Cup.
Elias gave Botafogo an early lead before former Barcelona and AC Milan forward Ronaldinho curled a free kick into the top corner from nearly 30 metres in the 28th minute.
Uruguayan Nicolas Lodeiro side-footed Botafogo back in front early in the second half but Luan grabbed a point for the Roosters in the 94th minute, taking advantage of hesitant Botafogo defending to score from six metres.
Cruzeiro made the most of the slipup when an 83rd minute goal by Ricardo Goulart gave them a 2-1 win at Criciuma, taking them ahead of Botafogo on goal difference. Both teams have 20 points from 12 games.