Li Xuerui of China plays against compatriot Han Li (not pictured) at the Badminton World Championship in Copenhagen August 28, 2014.

COPENHAGEN, Denmark - Saina Nehwal, India's greatest woman badminton player, and China's Olympic champion Li Xuerui have become embroiled in a sharp exchange of words before they meet in Friday's quarterfinals at the world championships.

After beating Japan's Sayaka Takahashi 14-21, 21-18, 21-12 in the third round on Thursday, Nehwal said that entry regulations should be changed to help reduce China's monopoly of titles.

"When so many Chinese are playing against one player they can work you out,'' Nehwal said. ``It would be better if three players per country should be allowed, not four.''

However, that view was firmly rejected by Li after her 21-9, 21-17 win over compatriot Han Li.

"Let Saina beat me first _ and then we'll talk,'' said Li, who has won seven of their nine encounters.

"Even if there are only three players per country, if she is not strong enough she can't win. This is her own problem.''

The last time Nehwal beat Li was more than two years ago, at the Super Series tournament in Jakarta, and the 23-year-old from Chongqing is a far better player now.

Whoever wins will have an unexpected opponent in Saturday's semifinals after defending world champion Ratchanok Intanon of Thailand was beaten by 16th-ranked Japanese player Minatsu Mitani 8-21, 21-12, 21-18.

Another contender from China is Wang Shi-Xian, the second-seeded All-England champion, who beat promising Vietnamese player Vi Thi Trang in straight games before going to watch her boyfriend Chen Long progress as well.

Chen, also a former All-England champion, beat Srikanth Kidambi 21-12, 21-10.

Lee Chong Wei, the world number one from Malaysia, was a 21-11, 21-12 winner over Ireland's Scott Evans as he bids to add the world crown to his collection.

Lee has more than 50 titles, though the world championship trophy has always eluded him. At the age of 31, this could be his last real chance.