Instructions
Battle the sirens that Zeus summons. Press the "O" button when you see an "O" appear above their heads to damage Zeus. The Chronos Rage and Atlas Quake spells work well against the sirens. Atlas Quake can hit multiple enemies in a pretty large radius. After you have killed enough sirens, an "O" will appear above Zeus. Go up to him and press the "O" button to move the battle to the next stage.
Use your roll ability to avoid Zeus's attack combos and lightning bolts, then use the Blade of Olympus's ranged attack (press triangle and L1) to damage and stun Zeus. When Zeus is stunned you may have time to move in and get off some normal sword attacks. Continue this pattern of dodging and attacking between Zeus's attacks until he rushes toward you and takes the Blade of Olympus.
Continue using your roll ability to circle Zeus and evade his attacks. Use the Blades of Athena to score a couple of quick hits on him from as long a range as possible. Do not engage in a long combo or you might not have time to evade Zeus's next attack. His attacks will be stronger and more varied with the Blade of Olympus, but they are not too difficult to avoid. The Chronos Rage spell is also useful in this phase to stun Zeus. Eventually, another sequence, enacted by pressing the "O" button, will let you get the sword back. You will have to repeat steps 2 and 3 again before moving to a new phase.
Use your Rage of the Titans ability to increase damage and defense. Zeus will surround himself in lightning that will damage you if you get too close, but with Rage of the Titans activated much of the damage will be nullified. Hold the square button or the L1 button to unleash powerful attacks while using Rage of the Titans. Chronos rage is also useful during this phase of the battle. After you do enough damage, a circle will appear above Zeus once more. Approach him and press circle to enact a final battle sequence.
Press the appropriate on-screen button prompts during the cinema sequence to finish the fight. You will have to press circle repeatedly to keep from being killed, and later you will have to press a single random button very quickly or you will be killed immediately. After entering all the buttons correctly, you will defeat Zeus.