It's obvious that black is a bit unfortable in this position. If only black could get his queen coordinated with his rook on a1, he might have some chances at counterplay via the a8-h1 diagonal. Now that his queen is under attack, Lasker had to find a way to get out of the line of fire of white's rook and still defend the knight on f8.
Lasker played 47... Qd6. Capablanca delivered the crushing and game-winning move 47. Qf8+! Lasker's cigar must have dropped out of his mouth and unto his lap. If 47... Qf8, then 48. Rh7 mate. Fritz suggested 47... Ra8 as a desperate way out, but 48. Qb7 is completely winning for white.