Swanson (0-1) took the loss Wednesday as the Mariners fell 1-0 to Cleveland, giving up one run on two hits over six innings while striking out five.
The right-hander made only one real mistake in first big-league start, but Jake Bauers put it over the fence for the game's only run. Afternoon shadows likely helped Swanson a great deal -- the two teams combined for only six hits -- but he still looked good and didn't display any nerves. Seattle hasn't yet confirmed he'll remain in the rotation, but assuming Swanson passed his audition and will continue filling in for Wade LeBlanc (oblique), his next turn would come in San Diego on Tuesday.