Note: Some of the analysis presented here is adapted from a discussion at Pete Tamburro's "Openings for Amateurs" forum (which requires registration prior to one's initially viewing it). Here is the applicable thread.

Now to the analysis...

1. e4 Nf6 2. e5 Nd5 3. c4 Nb6 4. c5 Nd5 5. Bc4 e6 6. Nc3 d6

7. Nxd5

7. cxd6 Nxc3 (7...cxd6 8. Nxd5 exd5 9. Bxd5 dxe5 10. Qb3, and the queen/bishop "battery" is annoying for Black) 8. bxc3 (8. dxc7 Qxc7 leaves White down a piece) 8...cxd6, and Black is fine.

7...exd5 8. Bxd5 dxe5 9. Qf3

This supposedly refutes Black's eighth move, but theory does not consider the following idea.

9...f5! 10. Bxb7 e4 11. Qb3 Bxb7 12. Qxb7 Nd7

By sacrificing a pawn to exchange light-square bishops, Black has gained control over the d3-square and hopes to soon plant the knight there. We now examine

A) 13. Qc6
B) 13. b4
C) 13. Qd5
D) 13. Nh3
E) 13. d4

A) 13. Qc6

13...Be7

13...Bxc5 14.Nh3, when 15. Nf4 or 15. Ng5 are a nuisance. The c5-square is best reserved for Black's knight.

14. Nh3 0-0 15. Nf4 Nxc5 16. Ne6 Nxe6 17. Qxe6+ Kh8

White's backward d-pawn remains a problem.

B) 13. b4

13...a5 14. bxa5

14. a3 axb4, and the a-pawn is pinned. 14. Ba3 axb4, and White cannot safely recapture (15. Bxb4 Rb8; 15. Qxb4 Bxc5). 14. c6 Ne5 15. bxa5 Nd3+ 16. Ke2 Rb8 17. Qa7 Bc5 18. Qa6 Qd4 wins material.

14...Rxa5

Black regains the pawn and maintains activity, as 15. c6 is disasterous after 15...Nc5 16. Qb1 Nd3+ 17. Ke2 Bc5 18. Nh3 Bd4.

C) 13. Qd5

Hoping to coax 13...g6 14. c6 Nf6, which would derail Black's Nd7-c5-d3 idea.

13...Nxc5

Not 13...Be7 14. b4 a5 15. c6, which would force the knight to where it lacks ready access to the d3-square.

We now examine

C1) 14. Qxf5
C2) 14. Qc6+
C3) 14. Qe5+

C1) 14. Qxf5

14...Be7 15. Nh3

This bolsters the f2-square in anticipation of ...Rf8.

15...g6 16. Qg4 Nd3+ 17. Ke2 Qd4 18. Qg3

Intending to answer 18...Rd8 by 19. Qe3. 18. Rd1 (anticipating Black's attack on the d-pawn) 18...Qc4, and White has no good defense to 19...Nxc1+.

18...Qc4

18...Bf6 is also not bad, with the idea of 19...Qc4 20. Kd1 Bxb2 21. Bxb2 Nxb2+ 22. Ke1 Nd3+ and 23...Rb8. Either way, White has difficulties.

C2) 14. Qc6+

14...Kf7 15. Nh3 Nd3+ 16. Ke2 Be7 17. Qc4+ Kf8 18. Rf1

Preparing 19. f3, to contest Black's control of the d3-square while opening a file against Black's king.

18...Qd6

Black stands well, as 19. f3 would give White another pawn island after 19...Ne5 and 20...exf3+.

C3) 14. Qe5+

14...Be7 15. Qxg7

15. Qxf5 would invite 15...Rf8 and 16...Nd3+.

15...Bf6 16. Qh6

16. Qg3 Nd3+ 17. Ke2 Qd4 18. Nh3 (18. Qe3 Qc4 19. Kd1 Bd4) 18...Qc4 19. Kd1 Bxb2 20. Bxb2 Nxb2+ 21. Ke1 Nd3+ 22. Kd1 Rb8.

16...Nd3+ 17. Ke2 Bg5 18. Qh5+

18. Qg7 loses to 18...Nxc1+.

18...Kf8 19. Kf1! Nf4

19...Nxc1 20. Rxc1 Qxd2 21. Ne2 (21. Rxc7 results in the deactivation of White's queen after 21...Qd3+ 22. Qe2 Qb1+ 23. Qe1 Qxb2) 21...Rd8 22. g3, threatening 23. h4 or 23. Rxc7.

20. Qd1 Qd3+ 21. Ne2 Rd8

Black has ample compensation and could regain the pawn at will, by ...Nxe2 followed by ...Bxd2. 21...Nxg2, intending 22. Kxg2 Qf3+ 23. Kg1 Rg8, would have been refuted by 22. Rg1.

D) 13. Nh3

13...Nxc5

13...Be7 14. d4 might enable White to improve over line E, since Black's bishop's would have already expended a tempo on the way to capturing the c-pawn.

14. Qc6+ Kf7 15. Nf4

15. Ng5+ leaves White defenseless after 15...Qxg5 16. Qxa8 Qxg2 17. Qd5+ Kg6.

15...Be7 16. b4

16. 0-0 Qd6 forces the exchange of queens, eliminating White's potential counterplay against Black's exposed king.

16...Nd3+ 17. Nxd3 Qxd3

White's light-square weaknesses persist. 18. Qxc7 can be met by 18...Rhc8, with ample compensation for Black.

E) 13. d4

To free the bishop and conceal the weakness of the d3-square, at the cost of creating possible outposts for Black on the c2- and e2-squares.

13...exd3

And now

E1) 14. Nf3
E2) 14. Qd5
E3) 14. Be3

E1) 14. Nf3

14...Rb8 15. Qxa7 Bxc5

Stronger than 15...Qe7+ 16. Be3 f4 17. c6.

16. Qa4

The only safe retreat that controls the f4-square.

16...Qe7+ 17. Be3 Bxe3 18. fxe3 Qxe3+ 19. Kf1 Rxb2

Winning, as 20. Re1 would be met by 20...Rf2+ 21. Kg1 Re2+ and mate next.

E2) 14. Qd5

14...Bxc5

It's not clear what Black has after 14...Nxc5 15. Qxf5 Be7 16. Nf3. With a Black pawn at d3, a knight at c5 loses much of its point.

15. Qxd3

15. Qxf5 Qe7+ would be painful. 15. Bg5 would be defused by 15...Be7, but not 15...Bb4+ because of 16. Kd1 Be7 17. Bxe7, when 17...Qxe7 would not be check. 15. Nf3 Qe7+ 16. Be3 0-0-0 17. Nd4 Bxd4 18. Qxd4 Nb6, with Black's retaining the extra pawn.

15...Qe7+

Protecting the bishop in preparation for a possible ...Ne5. Black's active pieces offset the extra "pawn island."

E3) 14. Be3

14...Rb8

14...Bxc5 15. Bxc5 Nxc5 16. Qc6+ Nd7 would deactivate Black's knight. There's no urgency to capture White's c-pawn.

We now examine

E31) 15. Qd5
E32) 15. Qc6
E33) 15. Qxa7

E31) 15. Qd5

15...Nxc5

15...Rxb2 loses to 16. c6, with a latent fork at e5.

16. Qxf5

16. Qc6+ Qd7 (Illustrating one of the points of 14...Rb8—to free the Black queen from having to protect the rook.) 17. Qxd7+ Kxd7 18. 0-0-0 Ke6, and White must work to regain the pawn; this is also the case for 16. Qe5+ Qe7.

16...d2+

Clearing the d3-square for the knight.

17. Kd1

17. Bxd2 allows 17...Rxb2, as 18. Qe5+ and 19. Qxb2 loses to 19...Nd3+.

17...Nd3 18. Qe4+ Be7 19. Bd4

The checks run out after 19. Qc6+ Kf8 20. Qf3+ Bf6.

19...Nxb2+ 20. Bxb2 Rxb2 21. Qc6+ Qd7

With advantage, for 22. Qa8+ Kf7 23. Qxh8 would lose to 23...Qa4+.

E32) 15. Qc6

15...Rxb2 16. Bd4

16. 0-0-0 Rc2+ demonstrates the value of the d-pawn.

16...Rc2

16...d2+ 17. Kd1 Qb8, and the rook is immune because White's rook would then be lost, but 18. Qe6+ makes a mess of things. The saner text move seems to maintain a persistent extra pawn.

E33) 15. Qxa7

15...Rxb2 16. Qa3 d2+ 17. Kd1

17. Bxd2 Nxc5 (preventing 18. Qxb2, due to 18...Nd3+), and Black's pieces would get very active.

17...Qb8 18. Qd3

To prevent 18...Rb1+.

18...Qb4

Threatening 19...Qa4+ 20. Ke2 d1(Q) mate.

19. Bxd2 Nxc5 20. Qe2+

White would lose material after 20. Bxb4 Nxd3.

20...Qe4 21. f3 Qxe2+ 22. Nxe2

White seems to have neutralized Black's initiative and obtain even chances.

Conclusion: 9...f5 appears to fully rehabilitate 8...dxe5.