Olejnik brilliantly foiled Frank Nouble in the first half and then pulled off an even more impressive stop to keep out a David McGoldrick header after the break, ensuring Peterborough were involved in a first goalless draw for 172 matches.
Their last 0-0 was also against Ipswich back in December 2009 but the hosts almost snatched this one late on, Tyrone Barnet and Lee Tomlin both missing excellent chances.
Ferguson said: "Bobby has produced two brilliant saves. They were both massive moments in the game, as we couldn't afford to fall behind.
"The first one was excellent but the second was something else. I felt sure it was a goal all the way, but Bobby threw himself to his left and got a great hand on it.
"The clean sheet is the positive I take out of the game but we were not clinical enough for the second successive match.
"You have to take chances in tight games. We had them but we couldn't put them away.
"I just wish one of them had fallen to Dwight Gayle, because he is the best finisher in the club, but at least it is another point gained.
"If we can win at Leeds on Tuesday night, we'll be out of the bottom three, and that would be happy days."