World number one Zhang Jike dug deep to reach the men's singles quarter-finals at the London 2012 Olympics, but the same could not be said of Timo Boll or Jun Mizutani.

Zhang was given plenty of problems by veteran Belarusian Vladimir Samsonov and looked in trouble when he slipped 3-2 behind.

But the world champion showed real guts in moving through the gears to claim the next two and set up a quarter-final clash with Honk Kong's Jiang Tianyi.

"I was prepared for a very tough match," admitted Zhang. "But I do not think there is anything to improve on; if I carry on playing like this I will win."

Samsonov felt nerves affected his opponent - something that made his inability to finish the job all the more frustrating.

"I am very disappointed," he said. "I had a feeling that he was a little bit nervous; there is a lot of pressure on Chinese players.

"I think at the end I tried to hit some shots too hard when I should have just played with a little more patience."

In the end, the defeat meant Samsonov was sent crashing out alongside Europe's other great hope Boll, who was beaten 4-1 by Romania's Adrian Crisan.

Another upset came on table two, where Denmark's Michael Maze swept aside third seed Mizutani.

In a quite incredible display, Maze dominated every game against his Japanese opponent and eventually won 4-0.

That set up an all-European last-eight encounter with German Dimitrij Ovtcharov, who cruised to a 4-0 triumph versus Austrian 40-year-old Chen Weixing.

Elsewhere, Zhang's next opponent Jiang almost became the second scalp claimed by world number 77 Kim Hyok-Bong.

Kim had earlier secured the result of the morning when he delivered a remarkable success for North Korea over rivals South Korea, beating world number 10 Joo Saehyuk.

He looked certain to repeat the trick as he moved into a 3-1 lead versus Jiang, only to have no answer as his opponent took the next three games, including the decider 15-13.

While the rest of the star names were struggling, number two seed Wang Hao - a silver medallist at Beijing and Athens - was easing to a straight-games win against Singapore's Gao Ning.

The evening was rounded off by victories for Taiwan's Chuang Chih-Yuan and Japan's Seiya Kishikawa, who will face Crisan and Hao respectively in the next phase.