Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
I have played a lot of games with Pantheon, and this is the build I usually prefer. I´m a typical Pantheon Midlane gamer, so this build is focussing on playing on the Midlane.
The Early-Game is so called easy mode. You don´t need to fear any Opponent at Midlane, Mordekaiser, Vladimir, Veigar, Ashe. All kind of Char´s get easy raped by Pantheon. The clue is Zoning your Opponent. On LvL.1 don´t use your Spear for Last-hitting, just use it for harrasment and Zoning. Your Opponent is in Range boom, Spearshot. When you reach LvL.2 you can Combine your skills, just go Spear-Shield-AutoHit-Spear. This Combo is taking more than half of the life a Squishy Champion usually has. When you reach LvL.3 you can go for the kill, just use Heartseeker instead of Autohit in your combination, and put an Ignite on your Opponent. Also Heartseeker passive makes Last-hitting Creeps easy, because you almost get every Last-Hit Critical.
Just jump in and Kick butt :D