Leaders Porto suffered a shock 2-1 defeat at Famalicao as Portugal's Primeira Liga became the latest league to return to action following the coronavirus stoppage on Wednesday.
An embarrassing mistake by Porto goalkeeper Agustin Marchesin three minutes after halftime gifted Famalicao the lead.
The Argentine sent an attempted clearance straight to Fabio Martins who rolled the ball into an empty net from the edge of the penalty area.
Jesus Corona fired Porto level in the 74th minute but the hosts regained the lead four minutes later when Pedro Goncalves left fly from 25 metres and his shot found a gap between Marchesin and the near post.
Porto also had a lucky escape in the first half when Pepe appeared to trip an opponent in the penalty area but then also fell over and the referee waved play on.
All matches are being played behind closed doors but videos posted on media websites showed an estimated 200 Porto fans gathering behind barriers outside the stadium, singing and waving flags. Most were wearing masks but they did not appear to be respecting social distancing guidelines.
Porto top the table with 60 points but could lose the lead when arch-rivals Benfica, who are one point behind, host Tondela on Thursday.
Earlier, a spectacular, swerving 30-metre shot from Lucas Fernandes gave Portimonense a 1-0 win over Gil Vicente in the match which got the competition under way.
"Football without the public in the stands is very strange, it seemed like a pre-season game," said Portimonense coach Paulo Sergio. His opposite number, Vitor Oliveira, agreed.
"We need the fans," he said. "Looking at what is happening elsewhere, where things are opening up, I think that football can have some fans, maybe 20% or 30% of the stadium capacity. Football without the public is not football."