Porto clinched their 25th Portuguese Liga title by beating arch-rivals Benfica 2-1 in a thrilling classico at the Stadium of Light, but had to celebrate in the dark.
Porto's players poured onto the pitch to jubilate at the final whistle but as the home fans filed out, the stadium lights were turned off and the sprinklers came on.
However, the cold shower did little to spoil the champions title party and they continued to celebrate in the dark. Porto coach André Villas Boas simply said: "We showed who plays the best football."
Fredy Guarin gave Porto a ninth-minute lead against their closest challengers which was cancelled out by a Javier Saviola penalty eight minutes later.
But Hulk restored Porto's advantage, also from the spot, after 26 minutes and this time they held on to establish an unassailable 16-point lead with five games to go. They have won 23 and drawn two of their 25 Liga games this season.
Both sides finished with 10 men - Porto's Nicolas Otamendi seeing red after 70 minutes with home striker Oscar Cardozo following him down the tunnel 14 minutes later.
"The important thing was to come here, play well, win and win the title," Hulk said afterwards. "Now we have to aim to finish the season undefeated while we are also fighting in the Portuguese Cup and Europa League."