"There were moments we didn't handle so well and that's the lesson for us," said Kearney.
"We did some really good stuff and some moments where we didn't execute how we would like.
"There were momentum swings and we lost our way a bit after 15 minutes and they had the upper hand. After half time we asserted ourselves so it's a tough one when you get a result like that."
The result continues a dire run for the Warriors against the Sharks, who have now won nine of the past 11 encounters between the two sides.
Cronulla went into the match in seventh spot on the premiership ladder and now sit just two points adrift of the Warriors, who could slip into the bottom half of the eight by the end of the round.
Doubters have been predicting the Warriors' decline all season and pessimists will mark this as the beginning of the late-season slide that has been a grim tradition since their last finals appearance in 2011.
But with nine games remaining in the regular season there is no need to panic, but this latest defeat lays bare the reality they need to find another level if they are to retain their spot in the top four.
The Warriors were clinical early on in punishing two Sharks mistakes, with Solomone Kata and Anthony Gelling scoring inside the opening 10 minutes.
The momentum changed with back-to-back penalties helping the Sharks before right centre Jesse Ramien scored after 15 minutes.
The Sharks then benefited from two questionable decisions through a no-advantage ruling in the lead-up to Lee running in their second try, before an obstruction call allowed Townsend to level the scores off the boot just before the break.
The Warriors clawed their way back in the second-half but their momentum was ruined by yet another tough penalty going against prop Chris Satae for an incorrect play the ball.
Both sides traded goals before Johnson banged over his one-pointer, with Sharks five-eighth Matt Moylan's attempt at reply charged down.
The bouncing ball was knocked-on by Simon Mannering and the Sharks claimed possession before Lee broke the Warriors' hearts with his second try out wide, off an apparent forward pass.
"We fought our way back and did a lot of good things but like the coach said we shouldn't have let it get to that," said captain Roger Tuivasa-Sheck.
"We had a lot of moments where we could have executed and put the game away but we let it get to that final call at the end and were unlucky."
The Warriors have some injury concerns with forwards Bunty Afoa (elbow) and Tohu Harris (knee) forced them from the field in the second half.
Sharks 18 (Jesse Ramien, Edrick Lee 2 tries, Chad Townsend 1/2 cons, 2 pens)
Warriors 15 (Solomone Kata, Anthony Gelling tries, Shaun Johnson 2 cons, 1 pens, field goal)
