YTTLJ Chapter 38
It is stated that ZWJ pulled back his own strength and ZZR take this moment to attack him sneakingly
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As these two people’s three palms struck each other, Zhang Wuji suddenly felt that Zhou Zhiruo’s palms were void of any strength. Zhang Wuji was stunned. “Aiyo, not good!” he thought, “After fighting ferociously with Liu Shu [sixth uncle] for more than 200 stances, she is like a lamp which oil has dried up. If I continued sending out my strength, she would certainly die on the spot.” In desperation, he hastily pulled back his strength.....
The fact that Zhang Wuji was injured by his own pulled-back strength was known to him and Zhou Zhiruo only. Others believed that Zhou Zhiruo’s power was so strange that Zhang Wuji was not her match. The spectators only saw that Zhou Zhiruo did not continue her claw and thus they believed that she spared Zhang Wuji’s life. As a young woman, she successfully defeated Yin Liting, Yu Lianzhou and Zhang Wuji; three prominent martial art masters of this age. Everybody believed that her martial art was simply too strange; totally beyond anybody’s comprehension.