Use evasion for the lava damage that baine does after he's been in lava. You only get the extra damage when his melee attacks land. Also dip into the lava yourself every 20 seconds. The 10k extra fire damage you deal with every swing is pretty significant and will shorten the fight a lot.
The knockback comes from a totem he throws on the ground. You want to shadowstep back to him, click on the totem and place the targeting reticle under him. If you throw the totem back to him it deals 5% damage to his life and makes him take 50% extra damage for 20 seconds. Blow cds there (combat is really good due to the damage you can pump out during AR/SB for that 20 second window).