– Wesley So added the coveted title of U.S. chess champion to his growing list of international super-tournament victories, winning a two-game, tiebreaking playoff in heart-stopping fashion Monday.

By winning the national championship, the 23-year-old grandmaster from Minnetonka continued to build the case that he has the best chance of any of his rivals of dethroning the world champion.

“He’s very hard to beat, very levelheaded, very practical, and he’s growing in front of us,” said grandmaster Maurice Ashley. “Imagine how strong he’s going to be in two years.”

So has won tougher international competitions than the U.S. Championship — which features America’s top 12 grandmasters — but he desperately wanted to earn this title for the first time.

“I really wanted to win this one this year … because it’s the strongest national competition in the world,” So said. “All the great [U.S.] players have won this one.”

So faced a playoff after he finished the nearly two-week tournament Sunday in a two-way tie for first place. The playoff with grandmaster Alexander Onischuk of Texas consisted of two “rapid” games in which each player had only 25 minutes on his clock for the entire game. So, playing with the white pieces, dominated the first game.

“Kudos to Wesley the way he created instant madness” that confounded Onischuk, said Ashley, providing live-stream commentary.

Onischuk, nearly out of time and completely out of defensive resources, resigned. With that win, So only needed a draw in the second game to win the championship.

In that game, the colors were reversed, and so were the players’ fortunes. So found himself on the ropes, down two pawns and edging closer and closer to running out of time on his clock, which would mean an immediate loss. Down to his last 18 seconds, So found a way to keep checking Onischuk’s king with his knight, and there was no way for the king to escape. That perpetual check forced Onischuk to concede the draw and the championship — and the first prize of $50,000.

“Today wasn’t easy at all, but I wasn’t expecting it to be,” So said, adding that his play in the tournament shows he still has “a lot to improve upon.”

“I’m just happy to have won this and to be able to say I’m the U.S. champion.”

So’s rapid rise has been spectacular. He came to the U.S. from the Philippines on a college chess scholarship in 2012 when he was ranked No. 99 in the world. A little more than two years later he broke into the world top 10, earning invitations to elite tournaments. At first he struggled against the world’s best players. At the 2015 Sinquefield Cup in St. Louis, he finished dead last in a 10-player field.

But So honed his game and gained confidence. Since last July, he has dominated elite international competitions. He is now the No. 2-ranked player in the world, behind only the world champion. At the U.S. Championship he extended his unbeaten streak to 67 games, one of the longest such runs in history.

So’s calendar for the rest of the year includes top-flight competitions in Azerbaijan, Norway, Paris, Belgium, Spain, St. Louis (again), Georgia (the country) and London.

By the end of the year, So hopes to secure one of eight spots in what’s called the Candidates Tournament. That tournament is likely to be held next spring, and the winner earns the right to play a head-to-head match against the world champion, Magnus Carlsen, for his title.