The pairings
Round 1, September 9th:
Carlsen vs Kamsky
Nakamura vs Aronian
Round 2, September 10th:
Aronian vs Carlsen
Nakamura vs Kamsky
Round 3, September 11th:
Carlsen vs Nakamura
Kamsky vs Aronian
Round 4, September 13th:
Kamsky vs Carlsen
Aronian vs Nakamura
Round 5, September 14th:
Nakamura vs Carlsen
Aronian vs Kamsky
Round 6, September 15th:
Carlsen vs Aronian
Kamsky vs Nakamura
In the first round Carlsen got little out of the opening against Kamsky, but played the last 20 moves of the game extremely accurately. Aronian was under some pressure against Nakamura, but just as it had petered out into a drawish position Aronian hung the exchange. Nakamura continues to be something of a giant killer against most top players except Carlsen, with 3-0 in wins against Anand, 4-3 against Kramnik, 2-0 against Caruana, 6-3 against Karjakin, and a decent 4-5 against Aronian.
After the first round Carlsen has a live rating of 2865.4, with #2 Aronian at 2796.6, that is a lead of 68.8 points. Carlsen's biggest lead on an official rating list was in April 2013, when he had 63 points down to Aronian.
In the second round Carlsen has his on paper most difficult game in the tournament, with black against Aronian. Nakamura has the chance to build on his good start with white against Kamsky, but they have only beaten each other once each and draw is the most probable outcome.
I absolutely cannot believe how badly Livestream is screwing up the coverage of this event. 
All these bogus rewinds are making what is superb commentary of startlingly combative games almost unwatchable.
Nakamura in the lead but now follows two difficult games for him, black against Carlsen and Aronian. Especially black against Carlsen has been tough for Nakamura, since 2010 he has +0 -6 =2 against the Norwegian, losing his black games this far in 2013.
After three decisive games of the four played in the tournament two draws would be no surprise today though. Kamsky has white against Aronian and just can't keep losing, while Carlsen's stats against Nakamura would begin to look unreal if he continues winning those games.
Two draws it was, and even if it was the first game Nakamura didn't win in the tournament it was probably his best game this far. If he beats Aronian in the next round he will be #3 on the live rating list, and less than five points from second place, but beating Aronian with black won't be easy. Another two draws in round four and Nakamura should be content.
Now that was quite impressive, another tournament win to Carlsen's long list of victories. +3 in only six rounds in a 2797 Elo average tournament less than two months before the title match, and a 74 point lead on the October rating list (the gap between Carlsen and #2 is bigger than the gap between #2 and #28).
Highest average rating ever with 2797, first round September 9th, with Carlsen, Aronian, Nakamura and Kamsky. 70 000 dollar to the winner. With one month and three weeks between this tournament and the title match it will maybe not be the best scheduled event for Carlsen, who has 7-0 in wins against Nakamura, 7-4 against Aronian, but 1-2 against Kamsky (six years since the latest loss though). Prediction: Nakamura +1, Carlsen +1, Aronian =, Kamsky -2. Playoff winner: Nakamura.