Re-painting drywall after patching leaves tones
Three things:

Yes, you were supposed to apply a primer.
Fresh joint compound and drywall soak up paint like crazy.  The primer serves to seal the joint compound and drywall and create a consistent surface.  However, you've already painted - and the paint will do the same thing - just not as effectively and you'll probably need to do a third coat.

Paint takes time to cure and changes color as it does
It takes about 30 days for paint to cure fully - and usually the color will deepen as it does - so after your 3rd coat let it set a week and see if it's starting to blend in.

Your paint may never match perfectly
Paint age matters - and no matter how good the technology, 2 cans of paint are 2 cans of paint.  Pro's who get multiple cans of paint at a time for a room will blend the 2 together before painting to ensure uniformity.  Obviously it's too late for you to do that - your old paint was dry - but worst case if you really can't stand it after it's cured - just paint the one wall with a new coat.  Having a whole wall be slightly off color won't stand out anywhere near as much as having a spot of paint off color.