China's Wang Hao had to go deep to beat Ryu Seung Min of South Korea in the fourth round of the World Table Tennis Championships on Thursday.

The reigning world champion defeated Ryu Seung Min, current number 13 at the world ranking, through seven games in 10-12, 11-6, 11-8, 8-11, 7-11, 11-3, 11-6. In a rematch of the Olympic final of 2004, which the South Korean won, Ryu Seung Min came back to 7-6 in the final game, but had to capitalize after that. Wang won the game 11-6 and became the first to qualify for the men's singles quarter-finals.

Wang Hao was relieved after his hard fought victory. "I was well prepared for a tough match against my rival, but I believe I' m a better player, technically and mentally. We haven't played each other in main competitions since 2008. Finally I got the winning result as I expected," said Wang.

"Every time I play against Wang I am extra motivated and excited," Ryu said. "Because a lot of people wish to see us play against each other. Today I had the opportunity to win. At the start Wang looked a bit nervous. When I was leading 3-2 I thought his mood was low, but mentally he is very strong."

Number two seed Timo Boll advanced to the fourth round. The German beat Robert Svensson from Sweden 11-9, 11-8, 11-8, 11-6. " It was solid performance," he said. "He is not easy to play against, risking a lot, playing hard topspins. There were not so many nice rallies. In the end I am happy to win the important points."

In the fourth round, Boll will meet his compatriot Dimitrij Ovtcharov, who defeated Seiya Kishikawa from Japan 11-3, 11-5, 11- 3, 11-5. "Of course we are good friends, so it's a little bit different situation," Boll said. "In the end we are professionals. We have to behave normal and try to focus on our games. We know each other very well, so it is not so easy for both of us to find good tactics to surprise the other one. It's going to be a nice match. I am ready and in pretty good form the last few days."

Ovtcharov was looking forward to the encounter. "We played many times against each other and we practiced a lot against each other, " he said. "We know each other very well. I think he won seven times and I won twice in the past. Of course he is the favorite. I am in good shape and try my best. It is important to win the first games to stay in the match."

Zhang Jike, Xu Xin and Chen Qi from China, Jun Mizutani from Japan and Vladimir Samsonov from Belarus were also amongst the last qualifiers for the fourth round.