The driver escaped uninjured after his eastbound vehicle tipped over in wet, breezy conditions.
It happened at the A8 roundabout next to the Kingston Dock houses near Tesco at 2.20pm.
The police, fire brigade and recovery vehicles were at the scene.
The eastbound side of the road was closed for several hours while the lorry was removed. Traffic was diverted through Port Glasgow, and tailbacks built up.