The Jambos were deducted that tally at the start of the season for going into administration but by the start of October had trimmed the deficit to just nine points.
But two goals from Kris Boyd secured the points for the hosts at Rugby Park and means Hearts have not won in the Scottish Premiership for seven games.
Locke said: "We are back to square one and that's the bottom line. That's the first set of games gone and we need to do better in terms of defending because the two goals we gave away today were so cheap it wasn't true.
"They were two long balls which were quite simple to defend but we didn't do it well enough. You can't give a player like Kris Boyd those types of chances because he will put them away.
"If we are going to give ourselves any chance in games we have to stop leaking goals like that.
"We can use the fact we are such a young team as an excuse but we can't keep making the same mistakes and it's important we learn from it."
Killie counterpart Allan Johnston was full of praise for Boyd following the 30-year-old's double secured a second successive win.
"I thought Boydy was exceptional," Johnston said. "When he plays like that he is unplayable. It wasn't just his goals, it was his work-rate as well. In the last five minutes, you saw him running back to win the ball back for the team.
"Scoring goals is the hardest thing to do and he does it consistently. I don't think there are many people who can do it as well as he can."