For the first time in the 2012 U.S. Championship, one player rests atop the leaderboard. With his win today in round five over co-leader GM Gregory Kaidanov, local GM Hikaru Nakamura took control of the tournament. With three wins and two draws, his four points are one-half point ahead of defending champion GM Gata Kamsky, who bounced back by also winning today. However, since the two top seeds have yet to play, both still control their own destiny.

Nakamura reverted to his more usual 1. d4 today, reversing his trend of advancing his king's pawn, which he had done to surprise opponents in rounds one and three. 

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Kaidanov played a Catalan system, but Nakamura offered a temporary pawn deficit to activate his pieces. After Nakamura regained the material, Kaidanov's pieces could only entrench themselves and wait for the breakthrough. That came in the form of the improbable 61. f5 and subsequent king invasion. Kaidanov's rook and bishop moved listlessly back and forth while his opponent's monarch played checkers on the dark squares, taking the scenic route from g5 to h6 to g7 to f8 to e7. Kaidanov conceded defeat and now sits in a four-way tie for third, and will need some help to win his first-ever U.S. Championship.

Kamsky, whose 51-game U.S. Championship unbeaten streak ended yesterday, began a new one today by winning in a fashion that echoed Nakamura's victory. 

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GM Varuzhan Akobian eschewed his nearly-automatic French Defense and played the cramped-but-solid Berlin Defense, known for forming a nearly impenetrable wall. But it was only a matter of time before Akobian's defenses collapsed, as Kamsky's knights finally penetrated his position, capping off the offensive with the devastating 31. Nf6+. Getting low on time (Akobian was down to two seconds several times), Akobian could not hold off the attack.

Third-seeded GM Alex Onischuk got back into the mix by winning a topsy-turvy game against GM Robert Hess. 

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The Yale freshman did not control his knights as well as Kamsky. Hess's initiative began to subside after 22. Nfd4, which he called the wrong knight. Onischuk rallied for an attack on the castled king, and offered two minor pieces for a rook to prise open Hess's position. Still, it would not have been enough if Hess had played 29. Kf1, since after 29...Rxe4 30. Ne7+ Kh8 31. Ng6+ seals the win for white. “With knights, you always have to be careful,” Onischuk said. Instead, Hess made the practical decision to bring his queen backward into the defense, but Onischuk's rook eventually found daylight and a route to pay dirt – the second-rank. Onischuk played Pac-Man with Hess's queenside pawns, forcing him to resign.

Joining Kaidanov and Onischuk on 3/5 and a tie for third place are GMs Alex Lenderman and Yury Shulman, who played an uneventful draw versus each other. Both have won once and drawn four times at the event.

A pair of slow starters won in round five to get back to even scores. GM Alex Stripunsky reverse-engineered his rook back to the first rank to win GM Yasser Seirawan's bishop. After losing his first two games, Stripunsky has 2.5 out of the last three.

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Joining Stripunsky was GM Ray Robson, who had a very promising middlegame according to Onischuk. With a light-squared attack on GM Alejandro Ramirez's king, he allowed the pressure to dissolve, only to later win a tricky rook-and-pawn endgame.

While the U.S. Championship took on a betting favorite, the U.S. Women's Championship did not break the three-player deadlock. IM Irina Krush, IM Anna Zatonskih and WIM Iryna Zenyuk are all still tied for first place with 3/4.

Zenyuk and Krush, who are good friends, could not commiserate much during yesterday's off day since they played today. Whereas Krush said earlier in the tournament that she would be careful not to use up valuable energy by preparing too much, Zenyuk said she spent seven hours studying for Krush yesterday. Still, that would not be enough to predict everything.

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“Irina (Krush) surprised me with her opening choice,” Zenyuk said. The game, a Semi-Slav Defense, ended in a draw by agreement on move 30 when Zenyuk repulsed Krush's rook invasion. “We didn't see any fireworks today,” Krush said. “At last year's championship, I was just lost out of the opening,” Zenyuk said of their past encounter. “Someone like Irina is really good at openings. I really believe that. I was really scared.” Zenyuk continues her best championship ever, currently fashioning a 2500+ performance rating, nearly 300 points above her actual rating. “I feel more pressure, definitely. But I don't think I'm going to change much.”

Zatonskih kept pace, but for the second game in a row, she entered a deep think early in the game. 

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Facing FM Alisa Melekhina's commonplace Sicilian Alapin, the defending champ could not decide between 6...Qxc5 or 6...Qxd1+. After 30 minutes, she chose the former, explaining that she wanted to keep pieces on the board for better chances of fighting chess. But Melekhina got the queens off the board anyway, obtaining a small but stable advantage of the queenside pawn majority. “She plays [the Alapin] also; it's tough to play against your own openings,” Melekhina said. “My position was so dangerous,” Zatonskih said. Melekhina pressed but settled for a draw by repetition in a double-rook endgame, as she feared the swift advance of her opponent's passed f-pawn. She expressed frustration at not being able to convert the full point. “Every time I thought I would gain a meaningful advantage, she found a simplifying continuation,” Melekhina said. “It's not just this game. In general I need to start winning.”

All three other games in the women's championship ended with white wins. WGMs Sabina Foisor and Tatev Abrahamyan both got a point to come within a half-point of the leaders. They beat WFM Alena Kats and WGM Camilla Baginskaite, respectively. Baginskaite is still without any points. WIM Viktorija Ni fought off infant-induced sleep deprivation to win her first-ever game at the championship, over IM Rusudan Goletiani, who has begun the tournament win-loss-win-loss.

Round six for the U.S. Championship and round five for the U.S. Women's Championship begins tomorrow at 1 p.m. Central, 2 p.m. Eastern. Come by the Chess Club and Scholastic Center of Saint Louis or tune in to www.uschesschamps.com for live commentary from WGM Jennifer Shahade and GM Ben Finegold.