Irelia is one of Nasus's easiest matchups because:
- Wither greatly reduces her damage output, because she is very auto-reliant
- You can match her sustain, which is her advantage in many matchups
- Irelia lacks the early damage to reliably harass you off the minion wave
- Irelia has no real ranged harass, so she can't do much to you when you are under your tower.
- Irelia's damage is suited for assassinating squishy opponents, not so much killing tanks.
Irelia was also your only opponent with any significant amount of armor (Kennen was AD, so no Zhonya's Hourglass).
Also, every lane on your team appears to have won, so you'd have a similar experience as most champions.
Just be careful against some of his harder matchups and certain team compositions. If the enemy can reliably harass and/or outsustain you, or just straight up kill you, you won't have a good time. Some champions to be wary of are:

will keep her Q on you the entire laning phase, so you can expect to take a double-proc when you go in for CS. Her sustain with her passive and Hextech Gunblade (or its components) is very high as well, so if you can't kill her in an all-in she will outsustain you. Her midgame is stronger then yours, so she'll be able to wreck any squishies on your team since she'll be able to freefarm in lane.
can range from easy to horrible, depending on the Riven's skill and whether she gets ahead. If she's good, expect to take a combo for every creep not under your tower and for her to have near perfect CS (to get the gold to snowball even without killing you).
isn't too hard to lane against because of Wither and his squishiness, but he will wreck you in teamfights if he gets Frozen Mallet to infinitely kite/peel you. And if you Wither him, then the ADC is free to wail on you.
will murder you later in the game. His damage is mixed (especially with Devourer), his DPS is far to high for you to heal, his meditate can block one of your Q and/or Challenging Smite will reduce your damage, and his ultimate lets him ignore attack speed and movement speed slows. You can't fight him, can't run from him, and can't avoid him if you are splitpushing.
can be pretty annoying since he's too tanky for you to kill at any point unless he really screws up, he can kite you with cleavers, he deals consistent mixed damage, he has percent health damage, and he scales similarly well. It's not really a bad lane since you can both farm, but Mundo can kill you early in the game before you get durability. Be careful for level 2 cheese, where he pokes you down with Q+E+AA when you CS and kills you when you are low.