The sixth seeded Mustangs travel to Chabot College next Saturday to take on the division's number three seed, San Leandro High. That game begins at 7 p.m.
Monte Vista has now won four games in a row, including a thrilling 34-33 victory over San Ramon Valley High in the regular season finale.
The Mustangs got off to a quick start in the rain on Saturday night, jumping out to a 14-0 lead in the first quarter against their visitors from Brentwood.
Heritage, the division's 11th seed, cut that lead to 14-7 at the end of the first period.
However, Monte Vista found the end zone twice in the second quarter to surge to a 28-7 halftime lead.
The teams traded touchdowns to make the score 35-14 at the start of the fourth quarter.
Monte Vista, which now sports an 7-4 record, found the end zone again early in the fourth quarter to take a 42-14 lead.
Heritage fought back, tacking on two late scores to close the gap to 42-28 late in the fourth quarter.
The Patriots scored one final time with less than two minutes left in the game and converted a two-point conversion. However, their rally fell just short.
Heritage finishes their season at 5-6.