open container

[redsauced]

Does opening a bottle of wine, but not decanting still beneficial in the same way? Went to dinner last night across town with a 2000 Sestadisopra Brunello di Montalcino. I know this needs 3 hours decanted, but I don't know these folks well enough to show up at 5PM for an 8:00 sitting. So I opened the bottle at home, and then drove across town, over the Golden Gate Bridge with the wine open between my legs. Sorry! There was no other way to hold the bottle upright and drive at the same time.
So I arrived at the dinner, put the cork back in, and asked the hostess for a decanter. At dinner a little later the wine went splendidly with pasta and pork loin, but I felt the wine was too tight. So, how do I deal with this in the future? And sediment aside, is there a huge difference between open and decanted?

Sorry if this sounds like an episode of "Car Talk" on NPR. There is a reason why I'm posting in the novice forum.