In the first round of the Sinquefield Cup, Magnus Carlsen played indifferently in the opening (against Gata Kamsky in that game) before responding to the pressure, rising to the occasion and winning the game. That's just what he did this time, too. Hikaru Nakamura held on against Kamsky in a hair-raising game to make a draw, and so if Levon Aronian could defeat Carlsen - albeit with the black pieces - he would create a three-way tie for first and thereby force a playoff.
With Carlsen in first and playing White, such a scenario would seem unlikely, but he nevertheless got into huge trouble. Around move 25 Aronian decided on the unfortunate plan of rounding up White's a-pawn. He was still a touch better after that, but he would have been seriously better, maybe strategically won, had he played 25...Nb5, aiming to put that knight on c3 and its partner in gallantry on d4. Aronian admitted missing 31.Ne1, eschewing the exchange to create a fortress.
So, a draw? Not quite. Aronian kept playing, and correctly so, but finally around move 47 he realized that there was no win to be had, and finally offered a draw. Many players would accept and collect all the rewards of taking first, but Carlsen felt safe and also recognized that Aronian was starting to lose the thread, and he continued. Sure enough, Aronian quickly collapsed, and Carlsen finished the tournament with a big exclamation point, finishing a full point ahead of Nakamura, two points ahead of Aronian and three ahead of Kamsky. (Games here, sans notes.)
What does the tournament mean for Carlsen's match against Anand? As far as openings go, the answer is probably this: absolutely nothing. How about Carlsen's form? That is a mixed bag, I think. Even taking his hiding his openings into account, he white games were awful: plenty of nothing in round 1 and very bad positions in round 3 (against Nakamura) and in this last game. The good news is that he still finished +3 and almost morphed into a computer whenever he was in trouble. His IPRs were very good, and here, courtesy of Ken Regan, are the IPRs for everyone in the event, both pro and con.
Carlsen: 2948 (+/- 90), his opponents 2679 +/- 200
Nakamura: 2797 +/- 150, vs. 2721 +/- 150
Aronian: 2654(!) +/- 230, vs. 2850(!) +/-150
Kamsky: 2535(!!) +/- 240, vs. 2765 +/- 170
The bottom line is that unless Anand plays very accurately with the opening advantages he gets, there's almost surely going to be a new world champion by the year's end.