For many years, this was considered the standard move here. In fact, some books on the Urusov Gambit continue to treat 6.Bg5 as the main line. But Marshall and Torre showed in this tournament that 6.Nc3! must be the preferred treatment, when Black cannot so easily play 6....Nc6 7.Qh4 d5?! because White retains a clear though slight advantage after 8.Nxd5 Nxd5 9.Qxd8+ Nxd8 10.Bxd5 Be6 11.Be4. The old adage of "Knights before Bishops" was never more true.
Also strong here for Black are 7....Bb4+!? and 7....Qe7+, neither of which is especially effective if White plays 6.Nc3! instead of 6.Bg5?!
According to Hermann Helms, this position was reached in another of Torre's games from the tournament, which does not survive, where White played 8.Bb3 Bb4+ 9.c3 Be7 =+. Perhaps Torre knew the game Tartakower-Shories, Barmen 1905, which went 8.Bxf6 gxf6 9.Bb3 Be6 (better is 9....Qe7+!) 10.Nc3 Bb4 11.O-O-O Bxc3 12.bxc3 Qe7 13.Bxd5 O-O-O =.
Also strong is 8....Bb4+!? 9.c3 Qe7+ 10.Be2 =+ as in Pilgaard--Christensen, Copenhagen 1989. White's position no longer justifies the loss of a pawn, and after the exchange of Black's Knight for the important light-squared Bishop, White's game is practically without hope.
Gabriel Velasco suggests simply 13....h6 because "the sacrifice 14.Bxh6? is unsound." Once Black plays Re8, however, he allows the defensive retreat Bf8 and helps to assure an easy defense against the King's-field sacrifice. Torre is always patient.
White has still managed to create pressure on Black's game due to his speedy development, which has allowed him to double Rooks on the open e-file. With this well-calculated move, however, Torre forces some simplification.
Threatening to trap the Rook with 23....Be6 and 24....Kf8.
Black activates his Rook and creates a passed pawn.
The best defense is to try for counterplay. White must grab the loose h-pawn with 27.Nxh4, establishing material equality. Black, of course, could then simplify to an advantageous minor piece ending with 27....Rc2 28.Rxc2 Bxc2, where the Bishop will be much better than the Knight in dealing with the passed pawns. But at least White would have some chances for a draw if Black is careless. Now the Black pieces coordinate to push the passed pawn forward.
White's pieces are far from the scene of action and can do nothing to stop the advance of Black's d-pawn to the queening square.