For more than three whole minutes, Thomas Snyder - twice a world Sudoku champion - sat contentedly on the floor of a Convention Center stage yesterday after he'd finished the final puzzle at the Philadelphia Inquirer National Sudoku Championship. It was the high-voltage $10,000 final round.

Behind him stood a large board with a tough advanced Sudoku puzzle he'd completed in a breakneck 4 minutes, 14 seconds. He looked relieved as his two competitors still worked to complete their boards, with the same puzzle. The next to finish was Tammy McLeod.

And that was when the numbers came crashing down, you could say, on Thomas Snyder.

He'd begun to walk over to congratulate McLeod on coming in second - a $4,000 award - when his board caught his eye. And there it was.

Two sixes in one column. You can't have two sixes in a column in Sudoku, a logic game you complete by filling numbers into blank squares. In a column, you can have the numbers one through nine.

Each.

And once.

Instead of congratulating McLeod for placing second, Snyder motioned to his Sudoku board to show that her (also impressive) speed of 7:41 made her this year's national Sudoku champion. In all, three boxes - or cells, as players call them - of his puzzle were incorrect.

McLeod was flabbergasted. Even through the soundproofing earphones the finalists wore as they worked, she'd heard the audience applaud Snyder. She was shooting for second - the position she'd won in the advanced-player final here two years ago. Last year, she came in third.

"I'm a little stunned," said McLeod, 32, a programmer for Google in Los Angeles.

Unlike several competitors yesterday, McLeod does not travel the world playing Sudoku for pots of puzzle gold. "The only competition I've ever done is this competition," she said. Yesterday's was the third annual championship sponsored by The Inquirer.

She'll receive $10,000, an iPod, and a seat on the United States team at the World Sudoku Championship, which will convene in April for the first time in its five-year history in the United States - in Philadelphia.

McLeod's generally high-flight performance slowed at one point, until she noticed empty cells she could fill instantly with the right numbers.

"When you play on a big board, it's hard to see the entire board when you're standing in front of it," said the diminutive McLeod, whose husband and 18-month-old daughter were watching from the audience. "But I wasn't stressed by it."

Indeed, not. Once she dispatched those little boxes, McLeod ripped through the puzzle. (Sharpen your pencils. The final-round Sudoku puzzles in the advanced, intermediate, and beginner categories will be published in next Sunday's Inquirer.)

As for Snyder: "I admit I had three minutes to check all the cells. What I checked was just whether all the cells were filled in. It was a mark of hubris."

Coming in third was Eugene Varshavsky of Lawrenceville, N.J., who registered as a walk-up contestant yesterday morning. He received $3,000.

In cavernous Hall B of the Convention Center, 646 contestants went after $25,000 in prizes, and 183 spectators solved the puzzles for fun. The event is billed as America's largest puzzle championship because of the number of players it draws in daylong timed competitions.

At the end of all the puzzle-solving, Brian P. Tierney, chief executive officer of Philadelphia Media Holdings, owner of The Inquirer, the Philadelphia Daily News, and Philly.com, unveiled a sign heralding the world competition here next year - an event he had sought along with Will Shortz, the New York Times puzzle editor and National Public Radio puzzle master. Shortz hosts the National Sudoku Championship.

Contestants sat at long tables for the different skills divisions. The largest number competed in the beginner category - 323 at red-clothed tables. White-clothed tables were for 254 intermediate players, and black for 69 advanced contestants. The spectators sat to the rear and sides, just at the outside of the contestant tables.

In each of three elimination rounds, the contestants were asked to complete three puzzles at their levels within a half-hour. After a lunch break they vied in age categories and by the towns of residence.

Most were from Pennsylvania and New Jersey, and the farthest one traveled was from British Columbia. Many were repeats from the last two years.

All were attempting to fill in the boxes of the numbers puzzle that, according to an Inquirer survey, is the nation's most popular. Upward of 170 million Americans have played it.

The object of the game, which employs logic but requires no math skill other than the ability to count from one through nine, is to fill in all 81 squares in a grid divided into nine three-by-three boxes.

Each row, column, and box must contain every digit from one through nine. Between 17 and 33 squares are already filled with a number in each puzzle, and players determine what to place in the rest of the cells to complete it.

"I was in the intermediate level last year, and I was totally skunked, so I am in the beginner this year," said Richard Weishaupt, a lawyer from Chestnut Hill, who noted that the puzzles were different when your play is timed.

"Welcome to my world," agreed Patricia Schmieg, a Council Rock High School South math teacher who'd overheard him as the competition began. "I'm methodical. The clock was ticking and I felt the pressure, and it blew my process." She was back, though, for more.

The youngest player was Jack Neumann, 8, of Chalfont. (He was the youngest last year, too.) The oldest was Edward Radbill, 93, a Philadelphian who's been playing two years.

Twelve-year-old Kevin Cunningham's entire family, from Havertown - a twin sister, a younger one, and his parents - were there to cheer him on with signs. Robert Borucki, a physician from South Carolina, competed, and so did his 15-year-old son, Davis, who walked off with a first-place $3,000 in the intermediate finals.

"I learned first," the elder Borucki said. "But he learned fast."

Sudoku Champions

Here are the winners of the third annual Inquirer Sudoku National Championship, in order and by division. First-place winners in the advanced, intermediate, and beginner categories also won iPods.

Advanced

1. Tammy McLeod, Los Angeles ($10,000 and a seat on the U.S. team at the World Sudoku Championship in April in Philadelphia). She came in third last year. She finished the final round in 7 minutes, 41 seconds.

2. Thomas Snyder, Palo Alto, Calif. ($4,000). He finished in second place last year, and is a two-time world champion.

3. Eugene Varshavsky, Lawrenceville, N.J. ($3,000). He joined the competition during walk-up registration yesterday morning.

Intermediate

1. Davis Borucki, Columbia, S.C. ($3,000), 8:42.

2. Andrea Kanner, Boston. ($2,000).

3. Vincent DeLuca, Swarthmore ($1,500).

Beginner

1. Naton Tsyrulnik, Shelton, Conn. ($1,000), 8:24.

2. Tori Spofford, West Chester ($500).

3. Rosalie Hooper, Ambler ($300).

Age categories

These contestants won $50 each for finishing fastest in rounds organized by age.

10 and younger: Hannah Barnhart

11-12: Rachael Hart

13-14: Xin Yu Zhang

15-16: Jonathan Kustina

17-18: Margaret Hock

19-20: Chris Narrikkattu

21-23: Brittnay Guld

24-26: Steven Conway

27-29: Thomas Snyder

30-32: Craig Helfgott

33-35: Lisa Haffner

36-38: Huan Wang

39-41: Charles Updike

42-44: Luigi LoTufo

45-47: Paul Winston

48-50: Karen Wheeler

51-53: John Hogan

54-56: Samuel Spear

57-59: Alan Resnik

60-62: Jeff Weiss

63-65: Fred Geldon

66-68: Carol Peckman

69-71: Ellen Du

72-74: Zizhi Zhu

75-77: Ruth Rainville

78-80: Shirley Miller

81 and older: Robert Shurley

Geography

Contestants also competed for their towns in a round of play. They received no monetary award. Their names will be published in an advertisement in next Sunday's Inquirer, as will the Sudoku puzzles for the beginner, intermediate, and advanced finals.

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Contact staff writer Howard Shapiro at 215-854-5727 or hshapiro@phillynews.com.