Well pantheon wins a lot of match ups early game so try to do your stun q then e combo as much as possible for tons of damage.

I feel these items are the best for pantheon because they allow him to get sustain and 2 slows the blood thirster at the end is for tons of damage

These runes allows for maximum attack speed/attack damage for tons of damage armor so they cant do tons of damage to you.

I take tp for maximum map control so you can do tons of damage all over the map cause you have tp and your ultimate ability. I take ignite for tons of damage and the debuff so they can't heal up the tons of damage you do.

I take these masteries for maximum cool downs and tons of magic pen for your w. Also maximum health so you can live if they are doing tons of damage. And maximum mana and mana regen so you consistently do tons of damage.