Southgate said: "Afonso has not been scoring, but he has remained focussed. If the lack of goals got to him, then he didn't show it.
"He has maintained the belief in his ability, and you could see that from his finish at Blackburn. It was fantastic. Now it's up to him to try to keep it going. Strikers tend to score their goals in runs, and Afonso is no different.
"Hopefully, it's the start of a rich vein for him."
Alves arrived at the Riverside Stadium from Dutch side Heerenveen in January with a formidable reputation, but has only eight goals to his name in 24 appearances to date, six of them as a substitute.
However, the quality of his finish at Ewood Park reflected the ability which persuaded Southgate to smash the club's transfer record to recruit him.
He said: "We know that Alves is capable of producing goals like that.
"Defenders find it hard to stop him when he gets a sight of goal. It was a clinical finish from him.
"That goal was important, not just for Afonso, but for the team.
"Now we have to continue to get the ball into the right areas, because Afonso will score goals given the opportunity."