Fresh from scoring a hat-trick in his side's 3-0 triumph over Sporting last week, Tello again proved decisive at Estadio Municipal de Braga.
The on-loan Barcelona forward latched on to a through ball from substitute Vincent Aboubakar and coolly clipped the ball over Matheus Nascimento with 17 minutes remaining.
Fourth-placed Braga were unable to respond as their six-match winning run in all competitions came to an end.
Porto have now triumphed in six league matches on the spin themselves and trail Benfica by a point ahead of the latter's trip to lowly Arouca on Sunday.
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