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