Cobi Crispin added 12 points for the Beijing 2008 bronze medallists, who proved too strong at the North Greenwich Arena.
They used an 8-0 run in the first quarter to quickly break the Mexicans' resistance.
A 10-2 burst early in the second period opened up a 31-12 lead and they capitalised on repeated turnovers to open up a 44-20 half-time cushion.
Floralia Estrada Bernal led some resistance from Mexico in the third period, but it was brief respite.
Australia capped their dominance by reeling off 10 unanswered points late in the fourth quarter to move as much as 62-35 in front, winning with ease despite shooting only 3/11 from the free-throw line.
Estrada Bernal grabbed 11 points and 16 rebounds for the Mexicans, who now go into the classification matches for 5th-8th place.
Merritt said: 'It was a really good performance. We came out not underestimating the Mexicans because they are quite a strong team as well so we came out there, respected them and played as hard as we can.'