Tendulkar passed the mark of 194 not out set by Zimbabwe's Charles Coventry in August last year and 194 by Pakistan's Saeed Anwar in 1997.
The 36-year-old is already the leading run-scorer in Test and ODI cricket.
Tendulkar's previous best was 186 not out against New Zealand at Hyderabad in November 1999.
India closed on 401-3, with captain Mahendra Singh Dhoni hammering 68 off just 35 balls as South Africa's bowlers toiled for no reward.
Highest individual scores in one-day international cricket:
1. 200 not out - Sachin Tendulkar, India vs. South Africa, Gwalior, February 2010
2. 194 not out - Charles Coventry, Zimbabwe vs. Bangladesh, Bulawayo, August 2009
3. 194 - Saeed Anwar, Pakistan vs. India, Chennai, May 1997
4. 189 not out - Viv Richards, West Indies vs. England, Manchester, May 1984
5. 189 - Sanath Jayasuriya, Sri Lanka vs. India, Sharjah, October 2000
6. 188 not out - Gary Kirsten, South Africa vs. United Arab Emirates, Rawalpindi, February 1996
7. 186 not out - Sachin Tendulkar, India vs. New Zealand, Hyderabad, November 1999
8. 183 not out - Mahendra Singh Dhoni, India vs. Sri Lanka, Jaipur, October 2005
9. 183 - Sourav Ganguly, India vs. Sri Lanka, Taunton, May 1999
10. 181 not out - Matthew Hayden, Australia vs. New Zealand, Hamilton, February 2007
11. 181 - Viv Richards, West Indies vs. Sri Lanka, Karachi, October 1987.