But how can the USA stop them if they're really determined to push Portugal out ?
Surely the USA declaring war, or sending military forces to defend the disputed territories, or even major sanctions, on Asian countries for taking back their rightful territory from some Nazi-friendly colonialist country wouldn't fly to US opinion (which is culturally anti-Nazi, fancies itself as anti-colonial, and has a strong isolationist undercurrent).
Moreover, if the USA oppose Asian takover of Portuguese outposts by military action or economical sanctions (and somehow the US opinion accepts it), the Reich might throw Portugal under the bus (knowing that Lisbon won't join the US bloc when it's so easy to invade from Spain, Salazar won't risk national suicide over Goa or Macao...) and instead woo China, India and Indonesia as friends which would be far worse than Portugal going full Linz.