Steven Thompson cancelled out Richard Brittain's opener soon after the restart but Lennon's side failed to build any momentum, Sam Morrow and an Ivan Sproule brace ensuring the visitors took all three points.
"We looked the more likely after getting the equaliser," said Lennon.
"What frustrated me was we let the individual errors affect us and stopped doing what we were doing 10 seconds before the ball hit the net.
"It was a group of players I didn't really recognise today, it rips me up inside to say Ross County wanted it more than we did.
"With the standards we set at the club and history we have, that is one of the worst performances I have seen."