patzer2: After 21...Ra7, Marshall calculated he could get away with playing 22. g4 because of the misplaced rook. However, he may have miscalculated and maybe shouldn't have played 22. g4!?
The combination looks like a winning double attack on the surface, but it doesn't seem to yield anything more than equality (maybe slightly less).
The pretty winning combination occurs only because Black blundered with the tempting 23...Rxe2? and missed the strong equalizing 23...Qf6!
After 22. g4 Nh4 23 Qh3 Qf6!, play might continue 24. gxh5 (if 24. Kf1, then 24...Ng7 =) 24...Rxe2! 25. Rxe2 Qg5+ 26. Kf1 Qxc1+ 27. Re1 Qc4+ 28. Qd3 Nf3 29. Qxc4 bxc4 30. Re8+ Kg7 31. Rd8 Nxd4 32. hxg6 fxg6 33. Rxd5 Nf3 34. Kg2 Rf7 = the position is level.
In the actual game continuation, notice that Black plays the awkward 24...Qf4 since 24...Nf4 fails to 25. Re8+! (now taking advantage of 21...Ra7) 25...Kh7 26. Qxh4 with a winning material and positional advantage.
The natural 25. Nd3! is a strong defensive and attacking move, resulting in the desperation check 25...Nf3+ (25...Qg5 also loses but is slightly better).
While 26. Kg2!? wins, stronger was 26. Kh1! avoiding any possible Knight checks after the Queen takes the Rook.
Marshall smartly avoids the error 27. Nxc1? because it throws away the winning advantage for only a near level position with even material after 27...Nf4+ 28. Kxf3 Nxh3 29. Re8+ Kg7 30. Nd3 Ng5+ 31. Ke3.
Also notice how Marshall uses the 28. h4! "deflection" to "break the pin" and complete the capture of the piece from the initial pawn fork 22. g4 (thanks of course to Black missing the equalizing 24...Qf6!).