The 19-13 win over England at Lansdowne Road made it three victories in a row in this year's Six Nations and set up the possibility of a Grand Slam decider against Wales at the Millennium stadium.
And O'Sullivan was quick to credit Ford for his contribution to the victory.
"Mike Ford must get a big mention for delivering a defensive performance like that," said O'Sullivan, who saw Brian O'Driscoll score a brilliant second-half try to add to 14 points from the boot of man-of-the-match Ronan O'Gara.
"Everybody's really believing what we are doing now and to go back two or three years we would not have won that game. We would have leaked a try or two at some juncture and the game would have slipped away from us."
Against England, despite the lead changing six times, the discipline instilled by Ford saw Ireland cling on even when they were put under severe pressure in the last 20 minutes.
"There were periods of the game when England were very dominant," admitted O'Sullivan.
"They played great rugby and were stretching the ball from touchline to touchline and very aggressively.
"We had to defend, not just heroically. We needed to throw our bodies on the line and know when and how to throw our bodies on the line. We showed great discipline and that is why they had very few kicks at goal."