Our starting position is usually reached after 1.e4 c5 2.Nf3 d6 3.c3 Nf6 4.Be2 Nbd7 5.d3 b6 6.0-0 Bb7 7.Nbd2 g6 8.d4!? We have looked at the opening phase of the 3.c3 line against the 2…d6 Sicilian in another challenge and now want to examine in greater detail the possible consequences of the pawn sacrifice 8.d4. White will try to open up the position at the cost of a pawn to exploit his slight lead in development.
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Typical for this opening is the intense battle for the center. White has just advanced the d-pawn to d4 with the goal of building of a strong pawn center. The immediate question that Black needs to answer is whether he should take the offered pawn and if so, using which move order.

8…cxd4 is the main move in this position. After 9.cxd4, White will often end up with an isolated d-pawn. This could be a factor in an ending. It is not clear who would benefit more from the opening of the c-file. The main drawback of this move is that Black no longer controls the d4-square with a pawn. Very good, but we are trying to do without this pawn exchange in our line of play.

8…Bg7 gets this bishop to the best square, but neglects matters in the center. White could now choose between the d4-d5 and the e4-e5 pawn advance. If you want to decline the pawn sacrifice on e4 with this move, you should probably exchange pawns on d4 first.

8…Nxe4 is not the most popular move in this position, but is quite logical. Black has done ok with the rare 8…Qc7 9.e5 dxe5 10.dxe5 Ng4 11.Qa4 h5, but the main line starts with 8…cxd4 9.cxd4. In the game Svidler-Kasparov (1997), White then got a promising position following 9…Nxe4 10.Nxe4 Bxe4 11.Ng5 d5 12.Bb5 Bg7 13.f3. Interestingly enough Svidler himself declined to take the e4-pawn when he had the Black pieces against Sepp in 2001. He survived after 9…Bg7 10.e5 dxe5 11.dxe5 Nd5 12.e6 fxe6 13.Ng5 Nc7 14.Bf3 Bxf3 15.Qxf3 Ne5, but we suspect that it shouldn’t be too difficult to improve White’s play. One main benefit of not exchanging pawns on d4 first is that Black will later be able to control the d4-square with a pawn from c5.

9.Nxe4 is clearly White’s only reasonable try to get compensation for the pawn.
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White hopes to pressure Black’s kingside before he can castle to safety.

9…Bxe4 is the only move that regains the lost piece.

10.Ng5 is White’s most aggressive continuation and attacks the audacious bishop on e4. White will also try to pressure the f7-pawn soon.
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Black has to look at all of White’s plans and make an important decision.

10…Bb7? looks like a reasonable move, but this bishop does not protect any of the dangerous diagonals leading to Black’s king from b7. White could expose the drawback of this move with 11.Bc4! Then 11…e6? runs into 12.Re1 and a sacrifice coming on e6. But the alternative 11…d5 12.Qf3! threatens mate on f7. Both 12…f6 and 12…f5 then allow a White knight to move to e6. Even worse is the otherwise desirable 12…Nf6?? due to 13.Bb5+. With this in mind, look for a better square for the attacked bishop.

10…Bf5? loses control over the key d5-square. After 11.Qb3 e6 12.g4, Black’s bishop on f5 would be trapped and Black’s king is still in a precarious situation.

10…Bc6 is a logical move, but has not been considered much in this position or in the similar position with pawns already exchanged on d4. This move comes to mind when one sees why 10…Bb7? cannot be played. Then 11.Bc4! d5 12.Qf3! Nf6?? loses to 13.Bb5+. Black can do better than this, but would still stand much worse. Note that other continuations such as 10…Bd5? 11.dxc5, 10…Bf5? 11.Qb3 and 10…d5?! 11.f3 are all unpleasant for Black.

11.d5 pushes back Black’s bishop. White this gains space in the center, the alternative 11.Bf3!? is also quite promising. Black then has to avoid 11…Bxf3? 12.Qxf3 Nf6 13.Qc6+ Nd7 14.Re1 with a strong attack for White. Following 11…d5, Black appears to hold the balance, e.g., 12.Qe2 Bg7 13.Re1 0-0. Note that Black could meet 11.Bc4 instead with …d5 12.Qf3 Nf6 13.Re1 Bg7.
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Play continues to be quite forcing in nature.

11…Bb7 is the only reasonable choice. It appears as if Black has now lost time, having to move this bishop again. But by playing 11.d5 White has shut down the dangerous b3-f7 diagonal and made it a little easier for Black to defend his position.

12.Bb5 pins the d7-knight and once again creates pressure against Black’s uncastled king. It is noteworthy that this line is not recommended after Black exchanges pawns on d4 at move 8. With the pawns on c3 and c5 off the board, White would now have the option to play 12.Qd4! in that line.
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Black has to carefully defend for his extra pawn.

12…Bg7 is the only playable move as it prepares to castle kingside next. Gaining this option was necessary since White’s idea was to play Qf3 next and threaten mate on f7. Note that 12…h6? instead could have led to disaster following 13.Ne6! fxe6? 14.dxe6 Bc8 15.Qf3. Then both mate on f7 and the rook on a8 are threatened. Black could stay alive in this line with 13…Qc8, but then simply 14.Nxf8 Kxf8 gives White a long-term advantage due to the bishop pair and Black’s weak e7- pawn.

13.Ne6 is a surprising turn of events. Black would be fine following both 13.Qf3 0-0 and 13.Qa4 a6 14.Bxd7+ Qxd7 15.Qxd7 Kxd7 16.Nxf7 Rf8 17.Ng5 Bxd5 18.Nxh7.
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Again Black has few reasonable choices.

13…fxe6 is forced as both the queen and the g7-bishop were attacked by this White’s knight.

14.dxe6 recaptures Black’s pawn and attacks Black’s pinned knight on d7.
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The tactical complications of the opening are soon coming to an end.

14…0-0 castles into safety and returns the extra pawn. This is the best choice now as trying to hang on to the extra pawn with 14…Bc8?? would lose a rook to 15.Qf3.

15.Bxd7 regains all sacrificed material and is the less ambitious capture. However, if White instead captures the knight with 15.exd7, Black could soon surround and win this pawn with 15…a6 16.Bc4+ Kh8 17.Be6 Bc6 18.Qg4 Ra7. White would get some compensation for the pawn following 19.Bg5 Bxd7 20.Rfe1, but Black maintains the edge with 20…Bf6!, e.g., 21.Bh6 Re8.
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Now material is even and a positional battle lies ahead.

15…Be5? does not accomplish much positive. White could now develop with 16.Bh6 and gain of time.

15…Rf5 moves the rook to a safe central square. Black now controls the d5-square a second time and has more room to operate on the kingside.

16.Qg4 gets the queen to an active square and gives White the option to move the c1-bishop to g5 again. White doesn’t have a convincing plan as Black controls the center with his two strong bishops. For example 16.Bb5 d5 17.Bd3 Rf6 allows Black to complete development with Qd6 and Raf8 next.
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Black’s light-squared bishop on b7 is now superior to its counter part on d7.

16…Qc7 moves the queen to a reasonable square and makes room for the dormant rook on a8 to get to f8. Black may later proceed with …d6-d5 to give the queen some breathing space. But White could now interrupt this plan with 17.Bg5. Then 17…Bf6 18.Be3 would leave Black’s pieces a bit awkward. White would next get the d7-bishop to c2 via a4 and pressure Black’s light squares on the kingside. Good, but we prefer a more active course on the kingside.

16…Qf8 aims to get the queen over to the kingside and fight for the initiative on that side of the board. If Black tried to activate his dormant pieces with 16…Qc7 and …Raf8 to follow, White could interrupt this with 17.Bg5 and pressure against the e7-pawn. This pawn is Black’s only weakness in this position. Black’s strong bishops and control over many center squares give him a promising position. Black now has a four against three pawn majority on the queenside and can try create a passed pawn at the right time by advancing with …d6-d5-d4. White’s four against three pawn majority on the kingside is much harder to turn into something useful. 

Play could now continue with 17.Be3 Qf6 and …Raf8 to follow. More challenging to Black’s plans seems 17.Bg5 instead. But after 17…d5 18.Rae1 d4, Black has to be preferred.

White doesn’t have many promising plans in this middle game. The best plan is to play for active play on the kingside. But it just seems to take too long to reach the desired setup with bishops on g5 and d3, a queen on g4 and the h-pawn advancing all the way to h5. Preventing this plan was Black’s main reason for playing 15…Rf5 and 16…Qf8 before doing anything on the other side of the board. Note that the immediate 17.Bb5 Qf6 18.Bd3 Re5 19.Bf4 Rxe6 20.Bg5 Qf7 is fine for Black due to the resource …d6-d5 to close the a2-g8 diagonal when needed. 
The final position seems to favor Black. White will have to look for improvements along the way. There are certainly several critical junctions in this line. At this time accepting the pawn sacrifice appears to be playable for Black. But he needs to defend like a hawk and must be ready to return material in order to get the king to safety at the right time.

This rarely played line without exchanging pawns on d4 and retreating the bishop to c6 may need to see more practical application before we can find out about its true merit. You should study the games by Russian Grandmaster Peter Svidler with both White and Black in this system to become more familiar with the general ideas and also to test alternate moves.