Cossu set up three good chances that fellow forward Antonio Di Natale failed to put away in the first half for the world champions, who were without a number of injured regulars.
Another debutant, defender Leonardo Bonucci, was less impressive as coach Marcello Lippi tried out a three-man backline that was not given an awful lot to do by their fellow World Cup finalists.
Forward Samuel Eto'o, who has struggled with Inter Milan recently, had a quiet game for a Cameroon side that will be looking to do better in South Africa after a disappointing African Nations Cup campaign that ended in the quarter-finals.
"It was a very useful match," Lippi told Rai television. "We saw the lads who I'd called up for the first time. Borriello had played for the national team before but it was the first time under me.
"Bonucci and Cossu played with good personality and authority."
But Wednesday's match was Lippi's last chance to size up his options before he names his squad for the finals.
"I'm satisfied with this match because Italy are world champions," Cameroon coach Paul Le Guen told a news conference. "They are a very experienced team with players who play with lots of composure."
"I wanted to review my squad this evening. We still have a lot of time to work before the World Cup. We have to be more effective in how we attack around Eto'o."
