3 defenders is perfectly fine if you play with a DMC and 3 or 4 midfileders, it works best with 3w-1-4-2 formation(DL.DC.DC.DR.DMC.ML.MC.DC.MR.ST.ST). This then gives you the option to change to 4 defenders later during the match if you deem it necessary!, in which case you then take off a MC or ST and revert to a 4-1-4-1 or 4-1-3w-2 formation., you are talking to the right person here as Ive been playing 3 defenders for the last 8 seasons!.