Signed from Ajax in June, Gravenberch opened his Bayern account 10 minutes before half-time, while 17-year-old Tel – an arrival from Rennes – added a superb second.
Sadio Mane made it 3-0 shortly after the restart with a simple tap-in, before substitute Jamal Musiala added a fourth.
Leon Goretzka then marked his first appearance of the season with a goal eight minutes from full-time as Bayern swept aside their third-tier opponents with little fuss.
Viktoria goalkeeper Ben Voll made a string of impressive saves in the opening half-an-hour but he was powerless to prevent Bayern from going ahead in the 35th minute.
The ball fell kindly to Gravenberch just inside the penalty area and he coolly slotted into Voll's bottom-right corner.
Bayern cemented their dominance on the stroke of half-time – Tel cutting in from the left and unleashing a fizzing strike into the far corner.
Mane extended Bayern's advantage in the 53rd minute with a close-range finish after he had been picked out by Serge Gnabry, before Voll made smart stops to deny the former Liverpool man and Musiala.
The latter was not to be frustrated again in the 67th minute, though, as he slid home after an incisive move involving Thomas Muller.
Goretzka, on as a substitute, then wrapped up the scoring late on with a crisp finish into the bottom-left corner after a surging run from midfield.