A Sri Lankan who has been on a world tour of badminton's backblocks for 10 months pulled off the first major upset in the London Olympics by eliminating eighth-ranked Kenichi Tago of Japan 21-18, 21-16 on Monday.

"This is the biggest win in the history of Sri Lanka badminton," Niluka Karunaratne said with obvious pride.

Also through to the last 16 were women's top seeds Wang Yihan and Wang Xin of China, who beat North American opponents with the minimum of fuss.

Like the Wangs, the top eight men's seeds drew only one opponent in their groups, virtually knockout matches to make the last 16. But nobody expected the exit to be shown to Tago, who was tipped to be a medal contender as he was an All England finalist in 2010 and semifinalist this year.

Bolstered by the fact he's always the underdog whomever he plays, Karunaratne said he was relaxed before meeting Tago for the first time. Midway through the first game he began to realize Tago was no quicker than him. Karunaratne was also starting to outlast Tago in rallies. The near-capacity crowd in Wembley Arena roared when Karunaratne took the first game.

"I don't know why the crowd was cheering for me but it was a great feeling," he said.

In the second game, Tago, who relies on his fitness to retrieve shots and turn defense into attack, looked increasingly flat-footed. The points became easier for Karunaratne, who finally won on his third match point, on attack. He dropped his racket, pointed to his father and mentor Louvie in the stands and thumped his heart three times.

"Winning this is incredible," Karunaratne said.

Then again, he's in the best form of his life — has been since October when he began traveling to qualify for the Olympics at his third attempt. He won his first international title on his father's birthday in Puerto Rico last November, and picked up more titles in Miami, Wales, Ugada and Iran. His ranking shot up from the 160s to a Sri Lanka-best ever 47.

In the last 16, Karunaratne is likely to face a friend, 10th-seeded Nguyen Tien Minh of Vietnam.

"If I play my best I can get another win," Karunaratne said.

The Wangs, also at their first Olympics, are good enough to look past the last 16 and at medals. Wang Yihan, who won the world championship in the arena last year, opened her games with a 21-8, 21-16 win over Michelle Li of Canada. No. 2-seeded Wang Xin beat Rena Wang of the United States 21-8, 21-6.

Also set to play on Monday are men's favorites, Olympic champion Lin Dan and top-seeded Lee Chong Wei.