– The U.S. Chess Championship tournament went from bad to horrible for Minnetonka’s Grandmaster Wesley So as he forfeited his game Friday for a rules violation.

The incident, which rocked the national championship competition, led him — and the Minnetonka family that has taken him in like a son — to reveal a tale of what the family called an ambush by his estranged mother on the eve of the tournament, an incident that created stress and distraction that threw him off his game.

“There are personal problems in my family,” So said after the forfeit. “Trying to fix them during this tournament caused a lot of stress and tension. It diverted a lot of energy from the board when I should be focusing on my game.”

So, the world’s No. 8 player, had lost three of his eight games before Friday’s forfeit.

The rules violation occurred only minutes after the ninth round began, when So was forfeited by the chief arbiter for writing a note to himself on his score sheet. Chess rules forbid a player from writing notes or anything other than the moves of the game, or things like a draw offer.

So said he had written a reminder to double-check and triple-check variations. He said it’s something he’s done before, including in this tournament. The arbiter said he had warned So twice earlier in the event that the notes were against the rules and that a subsequent violation would result in a forfeit.

As the shock over the forfeit reverberated at the Chess Club and Scholastic Center of St. Louis, the Minnetonka family that So lives with said it was time to explain publicly what has been behind his poor performance in the event.

Lotis Key and her husband, Renato Kabigting, took So, a 21-year-old Filipino, into their home last October after So decided to drop out of Webster University in suburban St. Louis, where he had a chess scholarship. He had just won the $100,000 first prize at the inaugural Millionaire Chess Open, and he wanted to pursue a chess career full time.

The decision to drop out did not sit well with So’s mother, with whom he’s had a difficult relationship since at least his midteens, when his parents and siblings moved from the Philippines to Canada. So stayed behind.

According to Key, So’s mother and aunt came to St. Louis and contacted So minutes after his arrival at a hotel. Key said they began, in strident encounters over the course of several days, to insist that he return to college or face losing complete contact with his family, including his sisters. At one point, So’s mother and aunt confronted him outside the chess club after his game, trying to grab his arm and yelling at him when he wouldn’t go with them to talk, according to Key and So. That led to an apology by So to the club for the scene, and a request that the mother and aunt be banned from the tournament site.

So’s mother, Eleanor So, could not be reached for comment.

Key said So’s mother admitted to her that So’s former chess coach at Webster had a hand in her trip to St. Louis to confront her son, including reserving a hotel room for her.

Key and So said the former coach, Paul Truong, was angry over losing one of the world’s top players from his team when So left Webster. “Wesley fell apart after that, knowing that his own biological family was working with his worst enemy,” Key said. “Paul will never forgive Wesley for leaving Webster.”

Key said that “three adults conspired to destroy a kid.”

Truong acknowledged that he had e-mail contact with So’s mother about a month before the tournament in which “she asked me if she could come down.” He said he replied that the tournament was open to anyone to watch. But he denied reserving a room or otherwise engineering their trip, saying that Key’s allegations are “absolutely 100 percent false” and that Key is manufacturing excuses for So’s losses.

Truong is well-known in chess circles as both the coach of the standout Webster chess team and for the messy legal dispute over the 2007 election for the U.S. Chess Federation executive board. After the election, a federation official posted a report saying that Truong almost certainly was the person who tried to bring disrepute upon a rival candidate by putting up fake Internet postings under that candidate’s name. Truong denied any wrongdoing at the time. But as suits and countersuits were settled, Truong’s chess federation membership was revoked and he left the board.

Meanwhile, So’s forfeit drops him into a four-way tie for fifth through eighth place. The tournament resumes Saturday and concludes Sunday, which can’t come soon enough for So. “Nothing is going right for me in this tournament,” he said. “I’ll be glad when it’s over. … There’ll be other U.S. championships. My goal for next year will be to win it.”