Rocco Quinn's double seemed to have handed the Staggies a share of the spoils - but Keith Lasley pounced amid hesitant defending to seal it for 'Well with eight minutes left.
"We didn't do well enough in the game to merit taking anything from the game," said a dejected Adams afterwards.
"If we defend as kamikaze as we did today then we won't get a result against a team like Motherwell.
"We have a bit of naivety about us at the moment and if we play like we did today against Inverness then we will be out the cup.
"We created openings and had chances but we have handed the victory to Motherwell."