The Rossolimo variation starts after 1 e4 c5 2Nf3 Nc6 3Bb5
one of the key points is to accelerate white's development. White typically plays 0-0 and starts to occupy the center. Hikaru picked 3..d6 which is less common than 3..g6 or 3..e6. Maybe he wanted to avoid Anand's prep.
And here is the position they reached after 20 Qc3! attacking f6.
White has achieved a winning position in 20 moves.
Knights cannot be captured.
If Black tries 20..exf5 21 ef5+ Kd7 22 Nf6+ Kc7 23 Qa5 Checkmate
If Black tries 20..exd5 21 exd5+ Kd7 22 dc6+ Rc6 23 Qd4! with checkmate threats.
If 20..e5 to stop Nf6+ then 21 Qa3! and c4-c5 will open up lines for White's attack.
Hikaru played 20..Rh6 but giving up the exchange did not work out.
Full game replay with annotations .
Great example where Anand quickly built pressure againt Nakamura using 3Bb5 against the sicilian
1. e4 c5 2. Nf3 Nc6 3. Bb5 d6 4. O-O Bd7 5. Re1 a6 6. Bxc6 Bxc6 7. d4 cxd4 8. Nxd4 Rc8 9. c4 [#] White has given up the bishop pair but has astrong grip on the center ( Maroczy bind c4 and e4) 9... Nf6 10. Nc3 Bd7 ( 10... e6 11. b3 Be7 12. Bb2 O-O 13. Qd2 Re8 14. Rad1 += ) 11. b3 b5?! fighting back against whites center but Black hasnt finished to develop his kingside ( 11... e6 ) 12. Bg5 Anand is happy to give up a pawn to accelerate hisdevelopment 12... bxc4 13. Nd5! This move prevents ..e6 and ..g6, therefore Black needs to find alternative plans. 13... h6? ( 13... Nxd5 the best move here 14. exd5 c3 15. Rc1 ) ( 13... e6 14. Nf5! ) ( 13... g6 14. Bxf6 exf6 15. Nf5! Be6 16. Qd4 ) 14. Bxf6 gxf6 15. Qf3 [#] ( 15. Nf5!? ) 15... h5 ( 15... Rg8 16. Nf5 Rg6 17. h4 Qa5 ( 17... cxb3 18. axb3 [%csl Ga6] ) ( 17... e6 18. bxc4 knights cannot be captured ) ) 16. h3 Bh6 17. Nf5! [#] White knightsdominate the bishop pair and the black king is stuck in the center. White only invested 1 pawn to get a dream position out of the opening 17... Bf8 ( 17... c3 18. Qxh5 Bxf5 19. exf5 c2 20. b4 Kf8 21. Rac1 Kg7 22. Qg4+ Kf8 23. f4 ) 18. bxc4 ( 18. Nxd6+! exd6 19. Nxf6+ Ke7 20. e5! dxe5 ( 20... d5 21. Nxd5+ Ke6 22. Nf4+ Ke7 23. Rad1 +- ) 21. Rad1 ) 18... e6 19. Rab1! Bc6 ( 19... Rg8 20. Rb7 Rc6 21. Qxh5 Rg6 22. Qh8 Qc8 23. Rb2 a5 24. h4 ) 20. Qc3 knights cannot be taken, and White is targetting f6. Great attacking play by Anand. ( 20. Nxf6+! wins on the spot 20... Qxf6 21. Nxd6+ Ke7 22. Nxc8+ ) 20... Rh6 desperate measures ( 20... e5 21. Qa3 a5 22. Red1 h4 23. c5 dxc5 24. Nb6 Qc7 25. Nxc8 Qxc8 26. Qxa5 ) ( 20... exf5 21. exf5+ Kd7 22. Nxf6+ Kc7 23. Qa5# ) ( 20... exd5 21. exd5+ Kd7 22. dxc6+ Rxc6 23. Qd4 ) 21. Nxh6 Bxh6 22. Nxf6+ Ke7 ( 22... Kf8 23. Nxh5 ) 23. Nd5+! Bxd5 ( 23... exd5 24. exd5+ Kd7 25. Qf3 Kc7 26. dxc6 ) 24. exd5 e5 25. Rb7+ Kf8 26. Qf3 +- [#] White is an exchange up with a devastating attack 26... Rc7 27. Reb1 Qe7 28. Rxc7 Qxc7 29. Qxh5 Kg7 30. Qg4+ Kh7 31. g3 ( 31. Rb3 ) 31... a5 32. Rb3 a4 33. Rb4 ( 33. Rf3 Bg7 34. Rf5 ) 33... Qa7 34. Kg2 Bd2 35. Rb5 Bc3 36. c5! dxc5 37. d6 Bd4 38. Qe4+ Kg7 39. Rb7 Qa6 40. Qg4+ 1-0