Wait...what? There were no opportunity attacks at all in 1e or 2e. You couldn't act outside of your own turn. When it wasn't your turn, you'd watch the enemies run right past you without doing anything to stop them. There was a whole debate about how you wouldn't even turn around if the enemy ran around behind you so you'd just let them stab you in the back.
In fact, that was the reason 3e introduced Opportunity Attacks as a thing. A lot of people writing into Dragon Magazine and TSR saying "D&D doesn't feel real time. It feels like you get to acts for your turn and then you sit there ignoring everything until your next turn." That's also the reason the Immediate Actions became a thing. Also, the reason facing was removed.
Before 3e came out, we spent a lot of time arguing about making a house rule where you might be able to stop people from running past you somehow.
You were looking for the withdrawing from combat/breaking off from melee rules - or even the falling back ones
AD&D 1e DMG p70
"if characters or similar intelligent creatures are able to single out an opponent or opponents, then the concerned figures will remain locked in melee until one side is dead or opts to attempt to break out of combat."
That's pretty clear by the standards of AD&D. You literally can't leave threatened areas without using one of the rules to attempt to break out of combat. Of which there are two in the rules: Falling Back and Fleeing.
Falling back:
AD&D 1e PHB p104-105
"Falling back is a retrograde move facing the opponent(s) and can be used in conjunction with a parry, and opponent creatures are able to follow if not otherwise engaged."
Note it's explicitly falling back and retrograde (i.e. backwards) - you can't use it to go forward past someone. It also doesn't work terribly well unless you have allies who are marking the enemy.
If you want to break off from combat without falling back then it's DMG p70 I believe which "allows the opponent a free attack or attack routine." In other words and opportunity attack by another name.
From Holmes Basic (I'm working on a websearch throughout)
"A character may withdraw from combat if there is space beside or behind him to withdraw into. His opponent gets a free swing at him as he does so with an attacker bonus of +2 on the die roll, and shields do not count as protection when withdrawing."
Again, that looks like an opportunity attack to me. And you can't go forward through combat - just back or to the side.
It confused me too, but remember, opportunity attacks (possibly under a different name) actually started in Combat & Tactics for 2e.
Nope. It was just expressed differently. Combat and Tactics was just where it started to be expressed as an ability used by the attacker rather than part of the withdrawing from combat rules.