"I feel so strongly that we will qualify because I saw the players in the dressing room and they were angry," said Ventura.
"They know they can do better. It was a physical match which surprised us but we are going to do better."
The second leg takes place on Monday at the San Siro in Milan. The last time Italy failed to reach the World Cup was for the 1958 tournament in Sweden.
"There are still 90 minutes left to play," added Ventura, who took over from Antonio Conte after Euro 2016.
"It was a tough, physical match that could have gone a different way if we scored first.”
Roared on by a vociferous home crowd at the Friends Arena in Stockholm, Sweden put Italy under pressure with their direct style of play and Emil Forsberg went close with a curling effort that flew over the crossbar.
A game pockmarked by scrappiness was appropriately decided by an imprecise passage of play. Johansson latched onto Ola Toivonen's header from an Emil Krafth long throw to fire a shot that wrong-footed goalkeeper Gigi Buffon after spinning off Daniele de Rossi.
It was the perfect time for the AEK Athens midfielder to score his first international goal, having only come off the bench four minutes earlier.
"It's fantastic," beamed the 27-year-old. "I put my goal down to instinct. Great timing for my first international goal."