This is an amazing game played by Capablanca. I have been looking at this game for the last few days and didn’t find an obvious mistake or blunder by Black until he had a lost position. This game shows that how a better pawn island and slightly better king can be a decisive advantage in the hand of Capa.
Position after 20. Rb3!
Capa just wants to double his rooks on the b file and penetrate through to the 7th rank.
The most natural move to meet the rook battery on the b file, but this allows exchanges of rooks. As an exercise it is useful to try to find some alternate ways to play Black’s position and see if White can win.
21. Rab1 Rb8 22. Rxb8 Rxb8 23. Rxb8 Kxb8
Now we have position where Capa’s king is just one rank more advanced than his counterpart.
24. Kd3 Kc7 25. Kd5 Kd6 26. g4 Ke6
26. Kf5 might be stronger but here White has clear cut winning plan. That is to exchange the f pawn against Black’s f pawn and he will soon get a kingside majority, and if Black keeps the f pawn, which is what happened in the game, then Black soon run out of good moves.
27. h4 f6
After 27…Kf6 there is 28. f4 exf4 29. Kxf4 Kg6 and now Ke5 is winning.
28. f4! exf4
After 28…c5 then 29. fxe5 fxe5 30. g5 is winning due to the outside passed pawn.
29. Kxf4 h6??
A blunder in a lost position because this creates another square (g6) for White’s king to penetrate, though no other move can save the day.
Black resigned after few more moves.
Here is the full game in case you’re interested.