势均力敌

shìjūn-lìdí

[balance of forces; their strength and advantage of situation match each other] 双方势力相当, 不分高下

吕惠卿始谄事王安石...及势钧力敌, 则倾陷安石, 甚于仇雠。 --《宋史·苏辙传》