The US championships are ongoing at the Chess Club and Scholastic Center of St. Louis, and after six rounds, Wesley So is in first place, but right behind him are Fabiano Caruana, Hikaru Nakamura, Stanford student Daniel Naroditsky, and Varuzhan Akobian.

So has not been his usual rock-solid self. Sam Shankland had chances against him; Caruana probably had a winning endgame, but Akobian had a winning position, all of which So survived. We will see if he can pull off the expected victory. Caruana has won only one game with five draws. His win came at the expense of the five-time US champion Gata Kamsky, whose confidence has hit rock bottom along with his score of just 2/6, placing him next to last. In last place is Alexander Shabalov, with just 1/6. Nakamura has just one win, with no loses, and is still very much in contention.

In the women’s championship, defending champion Nazi Paikidze has rocketed into first with three straight wins, the last being over a main rival, Irina Krush. She has a half-point lead over Sabina-Francesca Foisor and a point lead over Anna Zatonskih and Krush.

Paikidze would have a full point lead if she was a little more diligent in her 124-move loss to Zatonskih. She had been defending well until she lost focus and fell into one of the many little traps in the endgame and lost.

Andover’s Carissa Yip, the youngest competitor, has had a difficult event with just 3/6, standing in eighth place. However, her sixth-round win came at the expense of Zatonskih. Zatonskih played a particularly bad game that Yip took advantage of in a very professional manner. In her other games, Yip’s play has been very uneven. We will see if she can right her ship in the second half.

Recent results: Newburyport CC March Swiss: 1st: John Elmore, 3.5-.5; Billerica March Swiss, 1st: Joe Kelly, 4-1; Waltham March G/5; 1st: Todd Chase, 7.5-2.5.

Coming events:April 14, Waltham Free Wild Card #42, www.WalthamChessClub.org; April 16, 57th Papa Gino’s (Scholastic) Open, www.MassChess.org/Events.

Answer to today’s problem: 1.Rxe7! Rxe7 2.Nf6+ wins material as 2…Kh8 3.Qc8+ Re8 4.Nxe8. Even worse is 2…Kf8 3.Qc8+ Re8 4.Qxc5+ Re7 5.Bxd4 wins even more material as 5…gxf6 6.exf6 wins the pinned rook and 6.Qc8+ next is unstoppable.

Chris Chase can be reached at BostonGlobeChessNotes@gmail.com.