The Bianconeri have improved significantly since Iachini replaced Serse Cosmi in December and are now just one point behind 17th-placed Genoa.
Three points from the Marassi could see Siena take control of their own destiny while defeat could foreshadow the end of their two-season spell in the top flight.
Iachini told acsiena.it: "We have prepared well for this game, as always, and we will try to take all the points without worrying about the maths.
"We will go out onto the pitch organised and ready to apply what we've prepared during the week. It's important to bring continuity to our results.
"We need to play the perfect game to get a result."
Striker Nicola Pozzi, on loan from Genoa's city rivals Sampdoria, is Siena's only injury concern but Iachini would not give away his starting XI too hastily.
"There is another training session before I decide the line-up and formation and I will need the whole group to be at their best and ready to go at any time during the game," he added.
Iachini also praised tomorrow's counterpart Davide Ballardini, calling him "a quality coach and a warm guy", but the Ravenna-born tactician's star has fallen slightly in Liguria over recent weeks.
A run of three straight defeats leaves the Rossoblu in pole position to be sucked into the bottom three, with influential midfielder Andrea Bertolacci unable to help due to a suspension earned for a red card at Fiorentina last time out.
Striker Antonio Floro Flores and winger Juan Manuel Vargas miss out through injury as Genoa bid for a first home victory over Siena since both sides reached the top flight in 2007.
Defender Thomas Manfredini told Gazzetta.it: "We all know that it's a very important match, but we're ready.
"There's a great awareness of our own abilities in the group and we want to secure a home win which could count for double.
"It would be really important for us and I'm sure the fans will get right behind us."