The Eagles started better at the Estádio do Dragão. Gianluca Prestianni had the first major opportunity, while Alexander Bah came very close to opening the scoring with a shot that Pablo Rosario managed to clear practically off the line.
(Video): Porto Wins O Clássico
Porto claimed the first O Clássico of the season after defeating Benfica 3-1 in a match that completely changed in a matter of minutes and ultimately confirmed the Dragons' extraordinary start to the campaign.
But just when Benfica appeared to be growing more comfortable, the hosts responded.
Gabri Veiga Strikes and Benfica Goes Down to 10 Men
In the 30th minute, Pepê found Gabri Veiga with an excellent through ball. The Spaniard controlled it before finishing with the outside of his right foot past Samuel Soares to score his fourth goal of the season and give Porto a 1-0 lead.
Four minutes later, another major blow arrived for the visitors.
Clément Lenglet received his second yellow card following an incident involving André Silva, leaving Benfica with 10 men.
Despite being a man down, Marco Silva's team refused to surrender and found its reward in the 51st minute. Prestianni delivered an excellent cross and Bah arrived to get there first and turn the ball home for the 1-1 equalizer.
O Clássico was wide open again.
Porto Responds and the Birthday Boy Seals It
Porto's response, however, was immediate.
Pablo Rosario found André Silva, who laid the ball off for Victor Froholdt, and the Dane finished first time to restore the Dragons' advantage.
Just a few minutes later came the most special moment of the night.
Hwang In-Beom, who had entered the match for the injured Gabri Veiga, took advantage of a cross from André Silva, escaped his marker and finished with his right foot to make it 3-1.
He could hardly have chosen a better stage to score his first goal for Porto: on his 30th birthday and in O Clássico.
Benfica still tried to respond, and Vangelis Pavlidis came close to pulling one back in the 82nd minute, but Diogo Costa produced a spectacular one-handed save.
There would be no comeback for the Eagles.
Porto claimed the first O Clássico of the season, maintained its perfect start in Liga Portugal and delivered a powerful statement against one of its biggest rivals. Benfica, meanwhile, suffered its first defeat of the league campaign.
