White is threatening Qa7+ so Black has to take:

1... Rxf6 and now the position could well be one of those terribly difficult Dvoretsky-kind of puzzles where it says "Calculate the most convincing way to win for White." I suggest you try this one yourself without an engine running on the background. 2. Rc2!! In the game David played 2. Qa7+? but this should lead to a draw. He then tried too hard and even lost the game. 2... Ke8 Surprisingly, this is the only move that prevents a direct mate or the loss of Black's queen! 2... Rf5 3. Qa7+ Kd8 (3... Kd6 4. Qc7# is a mating construction to remember) 4. Qb8+ Ke7 5. Rc7+ Kd6 6. Rc8+ Ke7 7. Qc7# 2... Rf7 3. Qa7+ Kd6 4. Qb8+ Ke7 5. Rc7+ will be the same mate 2... Kd6 3. Qb6+ Ke5 4. Qb2+ Ke4 (4... Kd6 5. Qb8+) 5. Re2+ Kd3 6. Qc2+ Kd4 7. Qd1+ Kc5 8. Rc2+ winning Black's queen. 3. Rc8+! The immediate 3. Qe5 might be winning as well but Black can try 3... Rf3+! 4. gxf3 Qxf3+ 5. Kh4 Qh1+ 6. Rh2 Qb1 for example 7. Kh5 a4 3... Kd7 4. Rc1!! Because Black is facing the same threat he has to reply ...Ke8 again, so White has time to place his rook on the most convenient square. At first we tought that 4. Rc3 was best, but then Black can play 4... Kd6! and the line above where White won Black's queen doesn't work anymore, so 5. gxf6 (5. Qb6+ Ke5) 5... Qg6+ 6. Kf2 Qxg2+ 7. Ke1 Qh1+ 8. Ke2 Qg2+ 9. Qf2 Qg4+ and it's not clear if White can win. 4... Ke8 5. Qe5! Now this is just winning. 5... Rf3+ 6. gxf3 Qxf3+ 7. Kh4 Here there's no ...Qh1+. 7... Qf2+ 8. Kh5 Qf3+ 9. Kh6 Qf8+ 10. Qg7