Kate Upton -- Cleavage Goes M.I.A. When Cameron Diaz Shows Up

Cameron Diaz has an amazing and evil power -- the ability to make Kate Upton's massive boobs disappear.

As Cameron and Kate walked through the Sydney airport Friday -- not only was Kate NOT wearing a low-cut top ... she also pulled her jacket in a futile attempt to conceal her chest.

HUGE difference from Thursday when Kate was solo ... with her girls on full display.

This has been going on for weeks now -- every time Kate goes out with Cameron and Leslie Mann to promote their movie ... the rack gets put away.

Seems to us the spotlight is big enough for all the girls ... including Kate's.

On behalf of humanity, we say -- Cameron must be stopped!