Two late goals from Kelvin helped Porto keep their Liga Sagres hopes alive with a 3-1 over Braga.
Teenage substitute Kelvin struck twice within 10 minutes of coming onto the field for Argentina midfielder Luis Gonzalez.
It was the visitors who shocked Porto, taking the lead in the 23rd minute through striker Alan Silva.
Porto's Colombian striker James Rodriguez equalised eight minutes before half-time.
The scores remained deadlocked until Brazil midfielder Kelvin was introduced in the 76th minute.
His impact was almost immediate, scoring twice in three minutes to keep Vitor Pereira's men four points behind league leaders Benfica in the hunt for this season's league honours.