As the tournament to decide the U.S. chess champion reaches the virtual halfway mark, Minnetonka's Wesley So is in a two-way tie for first place, reflecting a sharp turnaround from his erratic performance last year.

So's aggressive play has been praised by experts as the most scintillating and entertaining of the tournament in St. Louis so far, and after five games he remains undefeated. So and fellow grandmaster Fabiano Caruana share first place atop the elite 12-player field, each with three wins and two draws.

Last year, in his first attempt at the U.S. chess title, So stumbled as distractions off the board affected his performance in the playing hall. An unexpected visit from his estranged mother rattled him, and over the board he became hesitant, missed winning opportunities and even forfeited a game because of a rules violation.

"Last year was a very difficult tournament for me," he said after his fifth-round win on Monday. "But as they say, the first is always the hardest."

This year, the 22-year-old So is playing with confidence. He began the tournament with a bang, sacrificing his knight to open lines of attack against his opponent's king and soon forcing resignation. On Monday, So doubled down, first sacrificing a knight and then sacrificing a rook on the very next move for just two pawns. Again, his opponent's king had nowhere to hide, despite the huge material advantage.

In a lighthearted mood after the victory, So said he had intended at the start of the game to play cautiously, "but then I couldn't control myself."

"That was a scorcher," said tournament commentator Yasser Seirawan.

"A massacre," commentator Maurice Ashley told So as he interviewed him. "You've had two of the most scintillating attacks in the tournament so far."

So also benefited from a dose of luck in the second round, when his opponent, in time pressure, missed a move that likely would have led to a win.

Tuesday was a rest day, and when play resumes Wednesday, So will have to face the No. 2 seed, Hikaru Nakamura.

"He's one of the best players in the world and I have a lot of respect for him, actually," So said. "He'a four-time U.S. champion. At the same time, I'm hoping for my first."

However, the path to the national title will be tougher for So than for his co-leader Caruana. So has a stronger set of opponents over the remaining six games than does Caruana.

And with players getting one point for a win and a half-point for a draw, the standings can change rapidly if a player goes on a winning or losing streak, or even a drawing streak. With four points each, So and Caruana currently hold just a half-point lead over the player in third place.

The final round of the 11-round tournament is on Monday, and if there's a tie for first place, a playoff will be held the following day with increasingly faster time controls until there is a winner.

The winner of the tournament earns a $50,000 prize and is crowned national champion, a title the late Bobby Fischer won eight times in eight tries.

Dennis J. McGrath • 612-673-4293