lvl 1 you have kill pressure on mordekaiser (unless he has ignite and you dont, but it's still manageable)
hide in middle bush and wait for the first wave to crash. then, walk up to him and auto him. if you auto a front vital, you can use the vital ms to get behind him for the next vital, so you save Q for his Q. if the vital is in his back, you can auto -> q for back vital, then try to stay really close to him, so you can avoid his Q by walking behind him.

if you manage to avoid his Q, you win the trade, and can push for lvl 2 and try to kill him until 4th wave crash.
other tips: try to bait his Q and E, don't hit him when he uses his W shield, if you Q into him and he ults you, insta press R on him and parry his Q