Jorginho had long been lined up to join Manchester City, but they were left frustrated as Chelsea's appointment of Sarri as their manager helped them take the Italy international in a £55 million ($72 million) deal from Napoli .
Guardiola and Man City are thought to be unhappy at losing the player they had long expected to sign, but Sarri believes his side needed him more, with the Manchester club having finished 30 points above them last season.
"I will try to explain all the [transfer] situation to [Guardiola] on Sunday," Sarri told reporters. "Jorginho is one of the steps to try to reduce the gap. He's only the first. But the rest is to work and [ignore] the market.
"We need Jorginho more than City, so it's right that Jorginho is here. Pep has great midfielders, central midfielders. Fernandinho is a wonderful player. The table of the last PL told me City 100, Chelsea 70 points.
"We have to try to reduce 30 points and I know only one way: to work. My job is this, to improve my players. I will try to do it. I don't think that every problem can be resolved by the market."
Sarri's first competitive game as Chelsea manager is against his friend Guardiola on Sunday, as the FA Cup winners face the Premier League winners in the Community Shield at Wembley.
The match sees Sarri against Man City, after drawing them last season with Napoli in the Champions League group stage. Sarri recalls that Man City were unplayable when his side faced them in October last season, going 2-0 down after 14 minutes in Napoli's match at the Etihad Stadium.
"Apart from the tactical point of view, I think it's very difficult for everybody to play against City," He continued. "Not only for one player or another. I played against City in November last season, in the best moment of City, of the season. And it was very hard, very difficult. The first 20 minutes was a nightmare, it was horrible."
Chelsea will be without a number of their top stars in the match on Sunday with the likes of Eden Hazard, N'Golo Kante, Olivier Giroud, Thibaut Courtois, Michy Batshuayi and Gary Cahill all having made the final weekend of the World Cup this summer.
Real Madrid had shown an interest in signing Hazard, but they have since cooled their pursuit over the hefty potential price tag. Sarri admits he has spoken to Hazard, but not about transfers as he awaits the return of his club's talisman after Sunday's game.
"I talked with him (Hazard) yesterday. We didn't talk about this [transfers]," Sarri added. "We talked only about 'can I arrive on Monday instead of Sunday?' In this moment there is no problem for Hazard."