Porto's shock home defeat to Estoril 24 hours earlier offered Jorge Jesus' men the chance to stretch their advantage at the summit and they did just that with a professional display.
Third-placed Porto are now seven points behind Benfica, with Sporting Lisbon, 2-1 winners at Rio Ave on Saturday, occupying second spot.
Benfica's winning goal against Vitoria came five minutes before half-time, courtesy of a beautifully taken strike from Lazar Markovic.
Rodrigo slipped a ball through on the edge of the area and Markovic timed his run perfectly before lifting the ball over the onrushing Douglas Jesus and tapping into the net.
Brazilian forward Lima ought to have put the result beyond doubt seven minutes from time, but somehow fired wide of an empty goal after rounding Jesus.
It mattered little as Benfica comfortably saw out the game and extended their unbeaten league run to 19 matches.
