The 20-year-old academy product has had a frustrating season, having been forced out of the first team picture for seven months through injury.
But Sims yesterday had a significant hand in the Saints equaliser, scored by another late sub, Manolo Gabbiadini.
“The important thing is that we need players that has to be really well prepared in all aspects," said Pellegrino.
“Josh is a young player who is getting better, who is home grown.
“I think little by little the connection between him and his teammates is better and I think it is good news for us."