User blog comment:UltraMegaDude/Will Rexy fight the Giganotosaurus in Jurassic World: Fallen Kingdom?/@comment-2001:5B0:45D7:C220:0:FF:FEBF:47C0-20180320210449/@comment-2001:5B0:45D8:B350:0:FF:FEBF:47C0-20180419161823

And I haven't even mentioned the pack hunting, yet. Giganotosaurus hunted in packs, so if there was a pack of Gigas on Isla Nublar, then T. Rex would be mincemeat.

Even if it was just one Giga, then T. Rex would also be eaten. The only case in which an adult T. Rex would have any chance of beating an adult Giga would be if the T. Rex was exceptionally large and fast, and the Giga was excpetionally small and slow.