Cueto's second-half double added to an earlier Sebastien Chabal effort and saw the Stockport men garner the advantage for the second leg on April 24.
Sale's first win since February looked in doubt in the first half as USA Eagles fly-half Mike Hercus - a late replacement for Charlie Hodgson, who failed a fitness test on his groin - conspired to miss four kickable penalties.
Despite shipping an opening try and losing both Cueto and substitute prop Barry Stewart to yellow cards, the Sharks - with former Scotland scrum-half Bryan Redpath coming off the bench to good effect - gleamed a scrum advantage in the final quarter, with French number eight Chabal to the fore.
Cueto's first was set up by a Chabal scrum break and, with Redpath and fit-again captain Jason Robinson ferrying the ball on with quick hands, the England wide man made it in at the right corner.
Cueto's second saw him out-muscle John Muldoon for the right corner again, but Andrew Farley's late try - built by his pack's willing maul - means there is still a lot to play for at Edgeley Park in a fortnight.