Little was dismissed in first-half injury time for a foul on Rovers player-manager Stuart Campbell, his second caution within the space of three minutes.
But Posh battled hard for their draw and Ferguson said: "The effort and commitment we put in with 10 men was fantastic.
"We were right on top in the first half and to lose a player at the end of it was disappointing.
"For the first booking, Mark has won the ball. I was further away from the second incident but perhaps he should have thought twice about making the challenge having just been cautioned.
"We gave away poor goals, which could have been avoided. But in the end we could have won because Craig Mackail-Smith had a wonderful chance and he normally sticks those away."
Source: PA
Source: PA