Ojha dismissed James Pattinson as his 100th victim in the morning session to bring an end to Australia's first innings at 262 all out at the Feroze Shah Kotla ground.
Ojha achieved the feat in his 22nd Test and, in the process, becomes the third fastest Indian to get 100 wickets behind legendary spinners Erapalli Prasanna (20 Tests) and Anil Kumble (21).
The 26-year-old from Orissa dismissed Pattinson on the first ball of his 27th over when the Australian pacer got the leading edge while playing for the turn and Virat Kohli completing a sharp catch at slips. Ojha finished with innings figures of 26.1-6-75-1 at an economy rate of 2.86.
Today's milestone has made Ojha the 18th Indian overall and world's 163rd bowler to get to the 100-wicket figure.
Ojha also becomes the fifth left-arm spinner from India to get to the milestone, the others being Bishan Singh Bedi, Vinoo Mankad, Ravi Shastri and Dilip Doshi.
Meanwhile, R Ashwin today equalled Anil Kumble's record of a 27-wicket haul in a four-Test series when he dismissed Australia's Peter Siddle this morning to finish with figures of 34-18-57-5.