How do you fend off Minecraft combos?

With normal 1v1 only with swords, it often happens to me that I'm grossly combined. In and of itself that's not bad, just how do I ward off this attack?

Is generally version-dependent

1.9+ a shield is required so that you can block using the off-hand.

1.8.9- Can you just block with the sword with a right click.

In both cases, however, you will slow down, which is problematic in a 1v1. I would rather focus on that. To get out of the combo, or to knock back the opponent yourself, so that you force him to heal as well.