While Agrawal was the toast of the day, eight-time world champion Advani fired the huge break against world bronze medallist Devendra Joshi in another quarter-final tie to reach the semis on an exciting day of big breaks.
Title contender Advani's effort eclipsed national champion Sourav Kothari's equally brilliant 494 earlier in the tournament, as he sealed a last four clash with former world champion Rupesh Shah, while Agrawal will take on twice world runner-up Dhruv Sitwala in the other semi-final.
Ten-time Maharashtra champion Agrawal got off to a dream start as he surged to a significant lead of 180 points at the end of the first hour of the two-and-a-half hour quarter-final against Kumar.
But Kumar, the 2011 Asian champion, initiated a fine recovery to lead 459-427 with crucial breaks of 86 and 68 with about 40 minutes remaining.
"I have been consistent from the beginning of the tournament and improved with every game. I dared to go for my shots while, I feel, Alok played under pressure and made quite a few mistakes," explained Agrawal.
"When Alok took that lead with two breaks, everything suddenly began going right for him. But I remained focused and managed to hold on. The breaks in the end proved decisive," he added.