On a difficult night for the sport's powerhouse nations, Americans Sean Rosenthal and Jake Gibb lost to lower-ranked Latvians Martins Plavins and Janis Smedins, ousting the United States from an event they had dominated.
Beach volleyball is only in its fifth Olympics. In the first four Games where it was played, Americans won the men's gold medal three times and Brazilians once. Those Brazilians were Emanuel and Ricardo, who now play in rival pairs.
In the last of the men's quarter-finals, Dutchmen Reinder Nummerdor and Richard Schuil beat Italians Daniele Lupo and Paolo Nicolai by two sets to nil (21-16 21-18) to set up a semi against Germans Julius Brink and Jonas Reckermann. Germany and the Netherlands entertain a fierce sporting rivalry.
Monday's results mean that at least one European team will be present in the final, improving on the previous best of silver for a Spanish pair in 2004. All other golds and silvers to date have been won by Americans and Brazilians.
"Of course we have all noticed that there are no US teams, but that means there must have been somebody to beat the US teams," said Brink.
"For sure for the media it's quite interesting but if you watch the teams playing it's just showing that the level of the sport is so strong and there are so many teams able to compete (with the Americans) and sometimes beat them," he said.
Plavins and Smedins will face Emanuel and Alison, and will need to produce an even more inspired performance to stop Emanuel's quest for a second Olympic title. He and Ricardo captured gold in Athens in 2004.
Emanuel and Alison beat Poland's Grzegorz Fijalek and Mariusz Prudel by two sets to one with a score of 21-17, 16-21, 17-15. Third sets are usually played to 15 points but the teams kept drawing level. The Brazilians saved a match point and needed two of their own to finally prevail.
"It was a fantastic game. Both teams never gave up. The energy coming from the stands, 15,000 people yelling for both teams, it was amazing. It was a great feeling. And I think we and Poland did a spectacular show tonight," said Emanuel.
Fellow Brazilians Ricardo and Cunha could never get into their groove against former world champions Brink and Reckermann. The Germans won by two sets to nil (21-15 21-19) in a match marred by refereeing confusion.
After one superb rally in the first set, the point was initially awarded to the Brazilians and then to the Germans after they complained that Ricardo had touched the net. The crowd booed the change and the atmosphere briefly soured.
A few points later, the referee became visibly unwell during a point, which had to be replayed after a new referee took over.
The Brazilians recovered more of their fighting spirit in the second set but could not subdue the consistent Germans.
It was the lowest point in Ricardo's Olympic career. He had won silver in Sydney in 2000 with Ze Marco de Melo, then gold in Athens and bronze in Beijing in 2008 with Emanuel. But the 37-year-old did not rule out another attempt in Rio in 2016.
"Let's wait one year after the other. The Olympic cycle is very long and we will see step by step," he said.
His young team mate Cunha, 29, gave him a vote of confidence: "If he thinks he's in shape, he's the best, so I will be glad to play with him in another Olympics."
Gibb and Rosenthal at first looked comfortable against their Latvian opponents, taking the first set, but Plavins and Smedins had a rush of energy and dominated the rest of the match. The final score was 19-21 21-18 15-11.
It was a crushing result for Gibb and Rosenthal, who came fifth in Beijing in 2008 and had been expected to fare better this time. The Americans did not hide their disappointment.
"It's a tough one to lose here this week. We've been playing really well lately and to come up short on what our overall goal was, it's a hard loss," said a sombre Rosenthal.
Fellow Americans Todd Rogers and Phil Dalhausser, gold medallists in Beijing, were knocked out by the Italians, Lupo and Nicolai, in a major upset in the round-of-16.
A quarter-final exit for Emanuel and Alison would also have been a big shock, but the Brazilians came back from the brink.
Emanuel, 39, is competing in his fifth Games. He is of such standing in beach volleyball that there is a larger-than-life statue of him at the entrance to the Olympic venue.
Alison, 27, is appearing in his first Olympics. A mountain of a man standing 2.03 metres tall, he shows his drive and emotion on court, pumping his fists at the crowds and encouraging his smaller, lither partner with bear hugs between points.
"In this kind of a match I can accept everything," a laughing Emanuel told reporters in response to a question about whether he feared being crushed by his partner.
"He can hold me, throw me away, if we're still winning, there's good vibrations between us, that's what we need to put our game on fire. He's the man to do that," said the veteran.