Launceston were left to rue a missed conversion in the final minute by Jake Murphy as they lost 19-17 at struggling Lydney in National Two South.
Lydney were at Launceston's Cornish rivals Redruth last week, but moved out of the relegation zone with the win.
Murphy missed a kick after Martin Kneebone's final-minute try.
"On a different day and with different conditions those things would have gone our way," said boss Cliff Rainford.
"It's quite a strong place for Lydney and we got dragged into their game plan a little, rather than sticking to our game plan and in the end that cost us."
Lydney led 16-0 at half-time and were 19-5 up late on after Liam Yeo's try for Launceston.
But the Cornish All Blacks staged a fightback with three minutes left as Ben Hilton went over and Murphy converted to make it 19-12.
Then in the dying seconds Kneebone scored a try, but Murphy's kick hit the post.
"It was always going to be one of those days," Rainford added.
"We had a few decisions go against us and they ran out winners in the end.
"Neither team really got control of the game."