KEG: Weak play throughout by Sterling.
5...Bc5: This moves practically invites 5. Ndb5. This could be avoided by playing 5...a6 (the Taimanov Variation). Perhaps the best move is 5...Nf6 (followed by 6...d6 [or perhaps better still 6...Bb4] if White plays 6. Ndb5).
6...a6: Now, having played 5...Bc5 Black must play 6...d6 or 6...Nf6. With the text, Sterling probably already had a lost game.
7...BxN: In this difficult position, 7...Kf8 was probably best. The Tournament Book suggests 7...Ke7 which works fine if White plays 8. NxB RxN (the only line considered by Rosenthal in the Tournament Book), but fails miserably against the much stronger 8. Bf4.
9. Bf4: This practically guarantees the exchange of Queens. White still has much the better---and perhaps a winning--position, but 9. Qg3 is stronger, and maintains White's bind on the position.
11...d5: As Rosenthal points out in the Tournament Book, this is "a mistake which compromises [Black's] game. The right move was 11...f5..."
12...Nb4: This move only makes things worse for Sterling. Relatively best was 12...Nd4, though Black is still in trouble.
14. Rd2: This move is good enough to maintain a winning advantage after the coming trade of Bishop and Knight for Rook and pawn, but 14. Bc5! was a killer (if 14...Bxc2 15. Re1!; and if 14...Nxc2 15. d6! Ng6 16. d7+ Bxd7 17. Kxc2).
15. a3: Marco should have played the powerful 15. d6, after which it is doubtful that Sterling could have held on very long. After the text, Marco has to win the ending with Knight and Bishop for Rook and pawn. A winning edge in theory, but not an easy task here.
18. Bd3: Marco should have played 18. Bd2 to avoid the exchange of Knight for his Bishop (18...NxB+) which in fact followed. After the text, it is not clear that Marco had even a theoretical win.
22...f5: Sterling could perhaps have held the ending before this mistake which fatally compromises his position. He had to sit tight with 22...g6.
24...b5: Another weakening move by Sterling, which soon costs him a pawn. After the text, his game is beyond repair. Best was 24...g6.
28. Rb6: This move is sufficient for victory, but even more crushing was 28. Bc6.
28...b4: This only hastens defeat. Best yet again was 28...g6.
31. Rb7: Marco inexplicably gives Sterling a chance to trade Rooks which would give Black a glimmer of hope. 31. Re4 was best.
31...Rc5: Sterling spurns the chance to trade Rooks, which was his only realistic hope.
33...Rcd8: This was tantamount to resignation. If he wanted to play on, he had to try 33...Rb8.
34. b5: As the Tournament Book notes, Black has no means of saving the game after this move. If 34...Rd3, White wins with 35. Kc2 (better than Rosenthal's proposed 35. Kc4).