Counter Panth
Let me explain something first. Pantheon was my first character i bought for IP 3 years ago when i started playing.I had no idea about his skills or anything,i just loved how he looks...
With that being said,i am not playing Panth because he is a beast,and recently i noticed more and more people complaining about him.
How to counter panth early game
Doran's shield and armor.You don't need ap or ad items 5 min into game anyway.He is going to OOM really fast.Try to freeze lane.He is going to be forced to poke minions instead of you if he wants gold.Every time he engage to kill minion,you attack him.Don't be scared to ask your jungler for help.If you freeze lane,he has to come to you,and there is your chance for kill.By the time he reach his turret range,he should be dead (with jungler's help)
If you have no trouble killing him,gank him couple times just to get gold advantage.
I hope this helps.