the best ways i have found to do this is to get consecutive perfects, or 1 perfect and 1 critical finish, preferably 2 perfects, for every round for the first 3 matches. Then try to get at least 1 perfect or critcal for every match onwards (the apprentice is a pain, but doable). For every perfect you get, you get 15000 points (so 30000 per match for 2 perfects), and 10000 for every critical finish. So 1 perfect and 1 critical is 25000 points.
You can throw fights if you dont, but if you havent lost a single round, the consecutive win bonus is better the further you go without losing. 1000 point for 2 consecutive matches, and additional 2000 for 2, 4000 for 3, 8000 for 4, 16000 for 5, 32000 for 6, and 64000 if you dont lose a single round. That comes to a total of 127000 points just from winning every round, meaning you dont get KO'd once.
2 easy ways i have found to gain this achievement are as follows:
Use yun seong and spam his forward Y, Y combo. This not only can get you easy perfects in the first few matches, but also drains your opponents soul gauge, due to the cpu blocking alot, meaning easy critical finishers (soul crush followed by the left bumper).
The 2nd way is to use astaroths cheap combo. This is done by holding diagonal down-back and holding X. Astaroth with charge up a low swing. When this connects, release all the buttons and press Y. He will perform an overhead swing causing a fair amount of damage, and knocking the opponent to the ground. Repeat until you win.
Using the methods above ive gotten over 450k several times with ease, so they should work for you.