Mexico led 3-0 within a half an hour on goals by Carlos Campos, Martin Galvan and Victor Manon.
In the second half, Galvan scored twice more goals to finish with a hat trick, and Luis Telles and Salvador Jasso also scored.
Mexico will qualify for the 2009 Under-17 World Cup in Nigeria with a win over Guatemala on Friday.
Qualification would end a skid for Mexico, which also failed to qualify for the 2008 Olympics (under-23) and 2009 Under-20 World Cup.
Costa Rica and Guatemala played to a 1-1 tie in the other Group B game.