Spain's defeat meant it was Romania and not them who secured direct passage to the finals in Japan and in a curious twist that angered the Spaniards the referee, Vlad Iordachescu, was Romanian.
Social media was quick to hint at dark conspiracy theories given the nationality of the man overseeing a qualifier involving a team in direct competition with his country's own World Cup bid.
And Spanish rugby federation president Alfonso Feijoo was in no doubt where the blame lay for Spain's shock defeat.
"Everyone who has seen the game will judge the referee. He gave 10 penalties against us, the result comes from that," he posted on Twitter before the federation went on to lodge a formal complaint.
Spain's coach Santiago Santos was equally furious.
"Our game was stopped continuously, the Belgians benefited from many more decisions," he said after struggling to calm down his incensed players at the final whistle with even the Belgian players coming to Iordachescu's rescue.
Later Sunday, the Spanish Rugby Federation said they had lodged a formal complaint to Rugby Europe and World Rugby.
"We have lodged a complaint with the European federation, with a copy sent to the international federation, for the refereeing commission to review the video of the match and judge whether the refereeing was deliberately in favour of Romania," said a statement from the Spanish body. "And if so, to act accordingly."
Spanish back Brad Linklater pointed to the "Belgian aggression and irregular tackling that went unpunished" by the man in the middle who was appointed by Rugby Europe.
Linklater did go on to acknowledge that his side "had not produced their best rugby".
A second guaranteed appearance in the rugby showpiece 20 years after their debut was within Spain's reach as they had routed Belgium at home earlier in the European group phase.
But a loss in a match they had to win, meant Romania and not the Spanish Lions secured direct passage to the finals in Japan.
The Santos-coached side still have a chance of qualifying through the play-offs.
They next face Portugal with the winner going on to play Samoa in a two-legged play-off for a ticket to join hosts Japan, Grand Slam champions Ireland, Scotland, and the Romanians in Pool A.
Spain came unstuck against Belgium's "best possible team" according to the host side's captain Jens Torfs.
Belgian coach Guillaume Ajac, who had fielded an inexperienced team in their away tie, recalled some established stars.
And the move paid off. Vincent Hart kicked them into a 12-0 lead at the break as their visitors at times appeared paralysed by the enormity of the occasion.
Spain put themselves back in the game with a try from Charly Malie in the 70th minute and a penalty 10 minutes from time but with a late penalty Belgium held on to spark anger among the Spaniards who turned their ire on the referee.
For Romania, the outcome in Brussels extended their record of competing at every World Cup since its inception in 1987, topping the table by three points from Spain.