ST. LOUIS – Wesley So will have to win a tiebreaking playoff Monday if he's to become the U.S. chess champion, and an exhausted college student with a class project due in the morning is partly responsible for that.

So, a 23-year-old grandmaster from Minnetonka, had a shockingly short game in the final round of the championship on Sunday. Instead of a typical four- or five-hour clash of minds, it was over in 17 minutes.

It was a draw — not what So was hoping for, and it left him waiting hours to learn his fate. But it turned out to be enough to secure a tie for first place and a spot in a head-to-head, two-game playoff.

The 14-move draw was a result of So's opening choice and his opponent's rare decision not to fight. So had the black pieces and chose an opening called the Berlin Defense, a line so hard for white to crack that it's nicknamed the Berlin Wall.

To So's surprise, his opponent chose not to even try. Grandmaster Daniel Naroditsky, a 21-year-old student at Stanford University, opted for a variation that left So with no choice but to make moves leading to an immediate draw. To do otherwise, So would have had to accept a losing position.

The choices of both players set off a raging debate among chess experts and average players about who bore responsibility for the tepid game — So for choosing the Berlin, or Naroditsky for refusing to battle.

Naroditsky admitted after the game that he was exhausted after nearly two weeks of grueling games. "To be frank, I'm a bit out of gas at this point," he said in a postgame interview on the live-stream broadcast from the Chess Club and Scholastic Center of St. Louis.

He also said he had a project due in the morning for his Mathematical Foundations of Computing class and was facing an all-nighter. He decided "it would not be a huge crime to do something that's perhaps somewhat unprofessional, but in my view is fully within my rights."

So said he had expected a fighting game and was caught off guard by Naroditsky's decision. Immediately after the game, and before Naroditsky had explained his reasoning, So wasn't ready to cast blame.

"He didn't do anything wrong," So said. "I mean I think his choice was reasonable. He didn't want to take much risk."

The draw left So's fate in the hands of his two co-leaders at the start of the round. If either of them had won their respective games, So would have fallen short. But 3 ½ hours later, one of them had lost and the other had drawn, ensuring that So would survive to battle again on Monday.

So's playoff opponent will be Alexander Onischuk, a 41-year-old Ukrainian-born grandmaster who lives in Texas, and who won the U.S. championship in 2006.

Onischuk conceded that So is the heavy favorite. Onischuk joked that before the tournament, he would have put his chances of winning it at 1 percent, and now he'd put his chances in the playoff at 10 percent. "I'll take it!"

Dennis J. McGrath • 612-673-4293