Dubov is white and must win. Nakamura is Black and must draw or win.
Opening was 1e4 e5 2Nc3 Vienna Opening. 
Position 1
Here the normal variation should be 12Nf4 Nf4 12Bf4 0-0 13 Qh5 with a += assessment. white's a bit better but the game goes on.
Instead, Daniil Dubov chose 12.Bd5! after thinking for 30 seconds which brings us here
Position 2
Now Black had to play 12..fg3+ 13 Ng3 Bd5 14 Qh5 Ne7 with White being better. the point of white's play is that Bd5 and Bc5 are hanging while Black hasn't castled yet. 15 Nd5 Qd5 16 Qd5 Nd5 17Rf5! 0-0-0 18c4! wins the bishop in c5. Black has only two pawns for a piece.
But Nakamura doesn't sense the danger and replied 12..Bd5 instantly
. He is definitely trying to play fast the opening. Logically the game goes on as this from diagram
12..Bd5?? 13 Nf4
Position 3
White is attacking the bishop in d5. if you retreat: 13..Be6 14 Ne6 fe6 15Qh5+ Kd7 16 Qc5 wins a piece. The bishop on c5 is loose.
So Hikaru spent 15 seconds and played 13..Ne7 on which Dubov replied 14 Qh5 c6 15Ncxd5 cd5 which brings us to the final position
Position 4
Can you spot the winning move ? with simple moves, Dubov achieved a winning position in 16 moves.
Answer is 16Ne6!
Position 5
Black is lost here. 16..Qd6 17Ng7+Kd7 18 Rf7! and White converted easily. Replay full game here.
Dubov won because he sensed this was a critical position at move 12 and invested 30 seconds to calculate and choose a dangerous move. Nakamura played instantly the obvious reply but this is lost by force. Speed is important but speed at all cost wasn't the right strategy.
Kudos to Dubov who won the event, after Nakamura eliminated Carlsen in the semi-finals. Dubov had to win against Sergey Karjakin who was also very strong in this format.
