The Foxes crushed Swansea City 4-0 at King Power Stadium without leading scorer Vardy to move eight points clear of chasers Tottenham.
The 29-year-old was sidelined after being sent off against West Ham United last weekend but Argentine forward Ulloa filled the void with a well-taken double, prompting the following response from a proud Ranieri.
"It's important because everyone wanted to see our answer without Jamie Vardy and that was a fantastic answer in my opinion," said Ranieri.
"I am very, very pleased with Leonardo, he scored twice, I am very pleased with (Jeff) Schlupp and all of my players.
"Leonardo made a fantastic performance, he jumped, he scored two goals, he attacked, he defended. Well done."
Riyad Mahrez and Marc Albrighton were also on the scoresheet in Leicester's defining victory in front of raucous home fans in the East Midlands.