|Date of birth||17 July 1992|
|Place of birth||Civitanova Marche, Italy|
|2011–2012||→ Fondi (loan)||23||(0)|
|2012–2013||→ Fondi (loan)||21||(0)|
|* Senior club appearances and goals counted for the domestic league only.
† Appearances (Goals).
Born in Civitanova Marche, Pacini started his career at Marina Picena, Porto Sant'Elpidio. In 2007 he was selected to Marche Giovanissimi U15 Representative Team for Coppa Nazionale Primavera. At the end of season he was signed by A.C. Siena and became one of the three youngest player of its Allievi Nazionali U17 team. Pacini was promoted to the reserve in 2008–09 season, and transformed from forward to a midfielder and then a right-back. The team was eliminated by Catania in the first round of 2011 playoffs.
In July 2011 Pacini left the reserve for his first professional team Fondi, where he met his future Parma team-mate Zsolt Tamási, Luigi Palumbo and Abel Gigli. Pacini made his professional debut in the first round of 2011–12 Coppa Italia Lega Pro. Pacini made 10 starts in 23 league appearances in 2011–12 Lega Pro Seconda Divisione.
In June 2012, Siena made a swap deal with Parma. It saw Pacini along with reserve team-mate Alessandro Iacobucci and first teamer Andrea Rossi were exchanged with Abdou Doumbia, Alberto Galuppo and Manuel Coppola. Pacini's loan was also renewed and Parma (along with Ascoli) also loaned Tamási and Palumbo (Cesena–Parma) to Fondi.
- "Primavera: inizia la preparazione" (in Italian). AC Siena. 29 July 2010. Retrieved 8 August 2012.
- "Comunicato Ufficiale N°63 (2006–07)" (in Italian). FIGC Settore Giovanile e Scolastico Marche. 27 June 2007. Retrieved 8 August 2012.
- "ALLIEVI NAZIONALI: La Rosa" (in Italian). AC Siena. ca. January 2008. Archived from the original on 12 February 2008.
- "Primavera: Fiorentina-Siena 1-0, bianconeri eliminati" (in Italian). AC Siena. 29 September 2010. Retrieved 8 August 2012.
- "Viareggio Cup: Siena-Spezia 4-2 Il tabellino" (in Italian). AC Siena. 22 February 2011. Retrieved 8 August 2012.
- "Catania-Siena 1-0 La Primavera esce dai Play off" (in Italian). AC Siena. 8 May 2012. Retrieved 8 August 2012.
- "Il Fondi piega l'Aprilia 2-0" (in Italian). SportLatina.it. 17 August 2011. Retrieved 9 August 2012.
- "Fondi, report sui primi allenamenti" (in Italian). Tutto Mercato Web. 24 July 2012. Retrieved 8 August 2012.
- Football.it Profile (Italian)