Unicron (planet form) vs. Death Star 1
First of all, both can destroy entire planets.
For those who didn't watch the original 1980's Transformers animated series, Unicron is a massive transformer who has two enormous tusks that can tear apart a small planet in half, the Death Star has one petawatt-range superlaser.
This takes place in hyperspace, Darth Vader spots an unidentified object. The object (Unicron) attacks the Death Star. Darth Vader orders the DS to fire.