- Bats Left, Throws Left
Salsi debuted in Serie A1 in 1997, winning 11 games for his native Parma while losing only 2 despite a 7.16 ERA. He was 1-0 with a 1.50 ERA in the European Cup that year, facing swedish team Leksand in the semi-final. In 1998, he went 7-4 with a save and a 5.56 ERA for Parma. He allowed 8 runs on 11 hits in 4 2/3 IP in the 1998 Baseball World Cup, debuting in Bologna against Cuba. Moving to Modena in 1999, his record was 4-6, 5.04. In 2000, the southpaw was 2-3 with a save and a 4.80 ERA.
Salsi moved to Serie A2 with Reggio Emilia in 2001 and would spend three years there. In 2001 he went 16-0 and also won 2 out of 3 playoff games, but lost Game 5 against Codogno. In 2002, he went 22-0 (with 2 saves), setting a league record for victories. He won his two playoff starts lifting Reggio Emilia up to Serie A1. In October, he also won the "A2 Coppa Italia" throwing for 10 innings against San Marino. At the end of the year he made his first comeback with the Italian national team. He walked 3 batters in 1 2/3 innings in the 2002 Intercontinental Cup but allowed no runs.
In 2003 Salsi struggled with a 2-7 record though he saved four games and had a 3.94 ERA for Reggio Emilia. He tied for 10th in Serie A1 in losses and was 6th in innings pitched (107 1/3).
Mattia moved to relief in 2004 and it paid off. He was 1-1 with 6 saves and a 1.92 ERA. He tied for 5th in Serie A1 in saves. In 2005, the Parma native was 4-3 with 7 saves and a 2.89 ERA. He tied Peter Nyari for second in saves behind Ilo Bartolucci. He was elected "Best Relief Pitcher" of 2005. He was 1-0 with a save and a 3.15 ERA in the 2005 European Championship as Italy won the Silver.
He was on the Italian reserve roster for the 2006 World Baseball Classic.
In 2006, Salsi went 4-3 with 8 saves and a 2.49 ERA. He led with 25 appearances and was 3rd in the circuit in saves. In the 2006 Intercontinental Cup, the southpaw was 1-0 with a 1.13 ERA, edging Sandy Patrone by .02 for the team lead. He outperformed former major leaguer Anthony Ferrari, the team's next-best left-hander.
Salsi was 3-2 with 6 saves and a 3.48 ERA for Parma in 2007, though he allowed a career-worst .331 batting average. He tied Emiliano Ginanneschi for third in Serie A1 in saves. Salsi appeared in four games for Italy in the 2007 Baseball World Cup, tying Chris Di Roma for the team lead. He had a 5.06 ERA and no decisions.