A problem in NP is NP-complete if

(B) A problem in NP becomes NPC if all NP problems can be reduced to it in polynomial time. This is same as reducing any of the NPC problem to it. 3-SAT being an NPC problem, reducing it to a NP problem would mean that NP problem is NPC.

http://gatecse.in/wiki/NP,_NP_Complete,_NP_Hard