Minnetonka Grandmaster Wesley So playing in the sixth round of the U.S. Chess Championship. (Dennis McGrath — Chess Club and Scholastic Center of St. Louis/The Minnesota Star Tribune)

ST. LOUIS – The national chess championship tournament turned out to be extraordinary for Minnetonka grandmaster Wesley So, though not in the way he would have imagined at the start.

In the end, he had quite a respectable showing. He won his final-round game Sunday to finish in third place. His 6.5 points left him only 1.5 points behind the winner.

Considering that he forfeited one game for a rules violation, which cost him a chance for another point, and says he was thrown off stride when his estranged mother showed up unannounced, it underscores what kind of threat he could have been if a storm hadn't swirled around him.

In retrospect, So said, winning the U.S. championship in his first attempt may have been too much of a reach.

"Probably my goals were too optimistic … for this tournament," the 21-year-old said in a livestream interview with grandmaster Maurice Ashley. "I'm just a starter [in] these elite events … I'm still not on their level."

That may seem like a curious comment from a player ranked No. 8 in the world, but his ascent has been so rapid in the last year or two that he is a relative newcomer to the most elite tournaments.

So said he picked "a wrong strategy, and it backfired." He played aggressively for the win each time, rather than choosing more cautious lines that would have sealed a draw. Playing too aggressively and losing is more harmful in the standings than accumulating points with draws and striking out for the win only when it's safe to do so, he concluded.

Tournament winner and new U.S. champion Hikaru Nakamura had no losses and agreed to six draws through the first 10 rounds.

Another takeaway for So will be to be careful about what he says about opponents. In the postgame interview Saturday, Ashley asked So about the rules violation from the previous day.

In that incident, So's opponent, grandmaster Varuzhan Akobian, complained to the chief arbiter when he saw So write notes on paper underneath his score sheet. The notes were reminders to double and triple check his analysis before making a move. Six moves in, So was forfeited for violating the rule against using notes during a game.

In response to Ashley's questions, So said Akobian "wanted the free point" for the win by forfeit.

"Wow, that's a big claim," Ashley replied, taken aback.

Nakamura went further in a tweet: "Very shameful and disrespectful comments by So about Varuzhan Akobian. Blame everyone except yourself for breaking the rules."

Asked about the reaction Sunday, So replied: "Who doesn't want a free point against me?"

That controversy aside, the forfeit will secure So a place in U.S. chess history for how rare it was.

"I was just shellshocked," said four-time U.S. champion Yasser Seirawan. "I have played chess for the better part of 40 years, and I've played I would say close to 4,000 tournament games … and in all of my experience … I've never heard of anybody being forfeited from a technical infraction regarding their score sheet."

Seirawan said he was certain So misunderstood the arbiter's earlier warnings and wasn't trying to skirt a rule.

For his third-place finish, So takes home $20,000 — or rather he would be taking it home except that he flies straight from St. Louis to Azerbaijan for a tournament that begins Friday and has an even stronger field than the one he just faced. The nine players he'll be paired against include five ranked among the top 10 in the world. Two of them are former world champions. And one is the reigning world champ.

Dennis J. McGrath • 612-672-4293