A late try from Tim Mathias denied the Bournemouth Lions a fourth successive win in National League Two South.
The Cornish All Blacks kept pace with the Dorset side throughout, and the reliable boot of Kieron Lewitt helped Launceston to a 27-22 win.
Bournemouth had the best of the first half and should have added to early scores from Sam Hardcastle and Frazer Wilford.
However, a rejuvenated All Blacks emerged after half time and sealed the victory with a drive-over try in the final minute.
Bournemouth Director of Rugby David Dunn said: "I think the first half went extremely well, we had the majority of the territory - and you could argue we should have had more points before half time.
"We went to sleep for fifteen minutes after half time and let them back into it. It all boiled down to a last minute try, and sometimes at this level you don't get the rub of the green."
The visitors made a perfect start when the Lions allowed the ball to bounce - and it fell kindly for the impressive Richard Bright, who opened the scoring after five minutes.
Bournemouth took the lead on sixteen minutes after a dominant scrum allowed Hardcastle to go over for an easy score. Stevenson was unable to add the conversion as his kick drifted wide.
The Lions pack were in control and another push set up the chance for Wilford to drive over for the home side's second try of the game. This time Stevenson was able to grab the extra two points with a perfect conversion from the touchline.
Launceston started the second half full of confidence, and Richard Friend took advantage of some lapse Bournemouth defending to cut the deficit within seconds of the restart. Lewitt's conversion brought the Cornish side to within a point of Bournemouth.
The Lions were struggling to build any momentum, and Lewitt scored two penalties to give the All Blacks a 20-15 lead. Things seemed to go from bad to worse for the Lions as Stevenson was given ten minutes in the sin bin.
However, the Lions made the perfect response, despite their numerical disadvantage.
Some intense pressure on the Launceston try-line brought a yellow card for Barry-John Chapman before a penalty try was awarded - giving Bournemouth a two-point lead thanks to Scott Chislett's conversion.
With time running out, the Lions had the opportunity to consolidate possession with a line-out deep in their own 22.
However, the usually-reliable set play was lost - handing possession back to the All Blacks. The visitors patiently pushed towards the line, and Mathias drove over to hand the visitors the win.
Bournemouth Lions: Richard Carrel (Ben Featherstone), Alan Manning, Gianluca Firetto, Tim Collier, Callum Forrest, Frazer Wilford, Charles Grace, Gavin Hart, Sam Harcastle, Ben Stevenson, Ben Stewart, Scott Chislett, Dan Connolly(Paul O'Brien), Andrew Edwards, Rory Trow (John Peart)
Cornish All Blacks: Tim Mathias, Aled Merdith, Neil Bayliss, Barry-John Chapman (Lloyd Duke), Ben Hilton, Mike Rawlings, Tom Rawlings, Josh Lord, Richard Friend, Neilson Webber, Liam Yeo, Sam Chapman, Lewis Paterson, Richard Bright, Kieron Lewitt