The battle of Tianwangshan means a key battle. A match like match point means that the game is very important, and winning or losing will affect the whole trend. It belongs to the battle of Tianwangshan, which means that the game is very crucial, and whoever can win can occupy an extremely favorable position. It's a bit like the old Huang Zhong in the Three Kingdoms robbing Dingjun Mountain.

The story of the Battle of Tianwangshan comes from the battle between Akechi Mitsuhide and Yuchai Hideyoshi after the change of Honnoji Temple during the Japanese Warring States Period. Tianwang Mountain is a very important commanding height. Whoever can climb up first wins. As a result, the monkey's army first climbed Mount Tianwang, and Akechi Mitsuhide committed suicide after the defeat.

Later, Japanese Weiqi circles preferred to use this word to describe the key game in Fan Qi's decisive battle, and it has continued all the time.

References:

Baidu Encyclopedia-Battle of Tianwangshan