Jeez, I'd call it a toss-up if the decent Mexican soldiers could of sent an invasion force into Washington D.C. and take the city in one day, or acutally set foot in the US heartland.
It was a totally one sided war.
Majors Battles/Seiges of the War which the US won:
Battle of Monterrey
Battle of Buena Vista
Seige of Veracruz
Battle of Cerro Gordo
Battle of Contreras and Churubusco
Battle of Molino Del Rey
Battle of Mexico City (Chapultepec)
What were some of the major battles that the Mexicans won?
Suprisingly, I found only one... and that was in August of 1846 when the US Army was thrown out of Los Angeles after a month of occupation, but only to return in January of 1847.