It's true that part of Viswanathan Anand's magnificent win over his bete noire, Levon Aronian, was home preparation, work he had done for his match with Boris Gelfand. But a good part of it he found on his own, including the sequence from 16...Nde5 through 19...f5, which sealed the win. With this spectacular game, which I've analyzed for you (see the link below), Anand joined Sergey Karjakin (who drew with difficulty against Hikaru Nakamura) and Magnus Carlsen (who defeated Pentala Harikrishna in a generally good but not perfectly smooth game) in first place. All three players are at +2 with 3-1 scores going into the rest day. Anand, who is working his way back up the rating list, will face Carlsen (new high: 2864.5!) on Thursday.
In other games, Loek van Wely was better early against Erwin L'Ami, and although that was the last game to finish it was the first to be decided. Anish Giri and Peter Leko drew a fairly placid-looking game - the only one of the round. Wang Hao outplayed his countrywoman Hou Yifan with White in a Nimzo-Indian, thanks largely to Hou losing the threat near the time control. Finally, Fabiano Caruana bounced back from yesterday's loss by defeating Ivan Sokolov on the white side of an Archangelsk.
The games (with fairly deep notes to Aronian-Anand) are here, and the tournament website is here. And here are the pairings for round 5, on Thursday (player scores are given in parentheses):