Mantei had four pitches. He had two fastballs, one of which regularly hit 95 MPH and occasionally hit 100, a sharpcurve and an occasional slider. He was also known to throw a knuckleball earlier in his career. Two issues concerning his play were his control and his ability for his arm to stay healthy. Between 1995 and 1996, Mantei had only pitched in 26 games for the Marlins. He missed the 1997 season due to injury and came back in 1998 to post an ERA of 2.96 in 42 games. After starting the 1999 season with the Florida Marlins and saving 10 games, he was traded to Arizona Diamondbacks in exchange for Vladimir Núñez, Brad Penny and Abraham Núñez. After posting 32 saves in between the two teams. Mantei was slowed by injuries in and, when a right-elbow injury ended his season in April and he underwent Tommy John surgeryligament replacement surgery. In, Mantei worked hard to regain his old form. Despite the fact that he missed a month in, he finished strong in the last three months of the season. He had 29 saves while posting a 2.62 ERA. Mantei missed most of 2004 after a surgery to deal with bone spurs in his shoulder. In 12 games, he was 0-3 with an 11.81 ERA and four saves. At the end of the season he was signed by the Red Sox. 2005 was yet another injury-plagued season for Mantei, as he only pitched 26.3 innings before being placed on the disabled list for the remainder of the year. Mantei was invited to the Detroit Tigers spring training camp in 2006 to make a comeback try. After suffering more arm troubles early in the spring, he left camp and was out of baseball until 2008. Mantei threw a bullpen session for the Detroit Tigers on January 11, and signed a minor league contract with them. However, after experiencing discomfort in his arm a few games into spring training, he was released and retired on March 4. In a ten-year career with Florida, Arizona, and Boston, Mantei owned a 14-18 record with a 4.07 ERA and 93 saves in 322.7 innings. He also compiled a 1.98 strikeout-to-walk ratio and a 1.39 WHIP.
Post MLB Career
On March 4, 2014, Mantei and his family appeared on the History Channel program Counting Cars, commissioning a custom-restored 1953 Chevy truck.
