Most of the guides I see show pantheon being a counter to Irelia, but in practice, he pokes me a few times, starts an all-in and I auto-stun-auto then q-RRR-auto while he tries to run (sometimes that last auto isn't needed) and he's dead. Why do guides say Irelia doesn't do that well against Pantheon? After Pantheon combos Irelia, he's basically a sitting duck.
Ideally Pantheon pokes Irelia before he combos her.. See, the matchup is described as bad for Irelia because it is bad for Irelia -> http://www.leagueofgraphs.com/de/champions/counters/irelia/diamond
Now, it isn't the worst matchup for Irelia and surely not the best of Pantheon, but overall it's clear that Pantheon does very well into Irelia.
I don't know much about the match-up, but if he's waiting until level 6 to try to kill you, then he is definitely fucking up.
Because he is an early champion and Irelia's early game isn't the greatest?
His passive can also negate an AA, allowing him to potentially decrease trade damage. It also blocks your Q, stopping your chase.
I think as long as you play safe and farm up some, he slowly loses his lead.
He probably didn't poke you enough before going in.
Because pantheon is getting outscaled hard later on and if he doesn't kill you in the early levels, your armor will surely counter him further on.
Because he automatically nullifies 2 of your autos which mitigates your all-in a lot, while he scales much faster, much earlier.
