XSUPREMEXSKILLZ
The Immortal Emperor
the teleportation thing happened during a time when Galactus was severely weakened, yeah. Heck, in Ultimates #7, he's still recovering from the affair.
That said, I'm not entirely sure who wins this fight, but just my 2 cents:
1. When Galactus was reverted to his devourer form, it was noted by Rodstvow that Galactus would devour all time and space until all that would be left is the First Firmament, (though how long this would take was undefined).
2. Devourer Galactus also has a potential multiversal feat during his battle with Scrier + Other.
3. Lifebringer Galactus is shown/implied to be far more powerful than devourer Galactus.
I'm not necessarily trying to say Galactus is multiversal + (there's far more evidence indicating otherwise,) just showing that in the context of the Ultimates series, this is meant to be the most powerful Galactus yet. Would he defeat Imperiex? No idea. So far the only forces confirmed/shown to be capable of defeating Lifebringer Galactus are Molecule Man (who is by far the most powerful character in Marvel currently, Imperiex is less than an ant to him,) and Logos, (the much more assertive/dominant stand-in for the Living Tribunal that stomped 8 celestials instantly and is the ultimate law within the Omniverse). Also the First Firmament, (the being who corrupted Chaos/Order in the first place).