How to defend Masters thesis?
It sounds as though your major contribution to expanding the extent of human knowledge is in showing how the new technique can be used to confirm results (X) which were obtained by the old technique. So when defending your thesis, you better be very sure that you show how this new technique enhances our understanding of X!!

If you are unsure how to best present this, talk to your advisor. In fact, even if you believe you know how best to present your contribution,  talk to your advisor! Take advantage of his/her experience and knowledge of the field to position yourself where your contribution can make the greatest possible impact. 

You need to prove that you have expanded human knowledge, so focus on how this is better than the old technique, not on how you have gotten exactly the same results. Again, your advisor should best be able to show you how to do this.