My Dad was showing me this rook endgame from Nikolay Minev’s book on rook endgames. Minev gives this as winning for Black after 77.Rb2+ Kc5 78.Rc2+ Kd4 79.Ra2?? Ra6 but I asked why White can’t play 79.Rc6. We came to the conclusion that it draws, and the engine says that 79.Rc8 and 79.Rc7 draw too.
In the game Gheorghiu played 77.Ra1? and after 77…Kb4! he resigned because after 78.Rb1+ Ka5 79.Ra1 Ra6 White is in zugwang, which must have been difficult to see. After 80.Ra2 Kb4 81.Rb2+ Kc3, the rook has run out of checking room.