Lucho Gonzalez and Steven Defour both scored to ensure that Porto started their Champions League campaign with a win against Dinamo Zagreb.
Despite the Portuguese side enjoying most of the early possession, it was Zagreb who came closest to opening the scoring with Helton only able to helplessly watch a Duje Cop strike fly inches wide of the post.
Porto should have taken the lead a few minutes later but Gonzalez failed to hit the target from close range after being picked out by Silvestre Varela.
However, Gonzalez was given the opportunity to atone for his mistake on the stroke of half-time and the midfielder composed himself to finish well from inside the box.
Zagreb provided much more of a threat after the interval and a superb save from Helton kept Porto ahead early in the second period.
Marcelo Brozovic was the next player to test the ability of Helton by stinging the goalkeeper's hands with a powerful strike from long range.
Porto confirmed victory in stoppage time when Defour broke free to calmly finish past Ivan Kelava.
Callum Mulvihill
