Recommendation for saving open bottle wine.

Your objective is to decrease the wine's exposure to oxygen. Dividing wine into smaller bottles is one of the ways to do this (but fill those bottles as high as you can. Another way to achieve the same thing is to use full bottles, but fill up the empty space with clean glass marbles (but be very careful when pouring from such a bottle).

Also do whatever you do as soon as possible after opening the bottle. That decreases the amount of time the wine is exposed to oxygen.

Whatever you do, realize that opening the bottle exposes the wine to the air, so what you do may make it last longer, but not as long as it would have if you didn't open the bottle.

Mark Lipton

The only thing to add to that is that it helps if you prevent oxygen getting into the wine before it is set aside for later. So if you are going to put a smaller bottle aside it you should decant slowly and carefully into the smaller bottle, and do it soon after opening the original bottle - certainly before you have started pouring glasses from the opriginal bottle.

That's what I am told at least - personally I rarely have the problem of leftover wine - and when I do I just stick the leftovers in the fridge and usually drink it the next day.