DiNardo was selected by the New York Mets in the third round of the 2001 MLB draft; he signed with the team in July 2001. In the summer of, DiNardo made his professional debut with the Brooklyn Cyclones, the Mets' Single-A affiliate. In 2002, DiNardo played for the Columbia Mets in the South Atlantic League, another Single-A farm team of the Mets. In 2003, he split time between the St. Lucie Mets and Binghamton Mets. He pitched well enough to warrant being selected by the Boston Red Sox during the Rule 5 draft on December 15.
Boston Red Sox
As is the requirement with Rule 5 selections, DiNardo would remain on the Red Soxmajor league roster during the entire 2004 season. He began the season on the disabled list and made his major league debut on April 23 against the New York Yankees in Yankee Stadium, retiring the side in order in the ninth inning. DiNardo spent much of the second half of the season back on the disabled list. With the 2004 Boston Red Sox, DiNardo made 22 appearances compiling a 4.23 ERA in innings pitched; he did not register a win or a loss. He received a World Series ring for his contributions to the 2004 World Series championship team. Having satisfied the Rule 5 requirement of keeping DiNardo on the major league roster during 2004, the Red Sox sent the pitcher to the Triple-A Pawtucket Red Sox to start the 2005 season. He was recalled to the major league club five different times during the year. For the 2005 Boston Red Sox, DiNardo appeared in eight games, compiling an 0–1 record with 1.84 ERA in innings pitched. In 2006, DiNardo made six starts in place of the injured David Wells. His first MLB win came on May 7, against the Baltimore Orioles. DiNardo spent a lot of time on the disabled list himself, due to a neck injury. With the 2006 Boston Red Sox, he appeared in 13 games, compiling a 1–2 record with 7.85 ERA in 39 innings pitched. DiNardo played for Italy at the 2006 World Baseball Classic. To prepare for the MLB season, he played for the Peoria Javelinas of the Arizona Fall League.
Oakland Athletics
On February 14, 2007, the Oakland Athletics claimed DiNardo off waivers from the Boston Red Sox. With the 2007 Oakland Athletics, DiNardo made 20 starts and 15 relief appearances, logging innings with an 8–10 record and a 4.11 ERA. During 2007, DiNardo had his first and only MLB hit, a single off of Matt Cain of the San Francisco Giants on June 10. For the 2008 Oakland Athletics, DiNardo made 11 appearances, compiling a 7.43 ERA with 1–2 record in 23 innings pitched.
DiNardo signed a minor league contract with the Kansas City Royals on December 17, 2008. He spent the last month of the 2009 season in the major leagues; these would be his final MLB appearances. For the 2009 Kansas City Royals, DiNardo appeared in five games, compiling an 0–3 record with 10.12 ERA in innings pitched. DiNardo again represented Italy at the 2009 World Baseball Classic.
Late career
On January 8, 2010, DiNardo signed a minor league contract to return to the Oakland Athletics; the deal included an invite to spring training. He played in the rookie-level Arizona League and for the Triple-A Sacramento River Cats, making 12 appearances with a 3.53 ERA and 2–5 record. On December 15, 2010, DiNardo signed a minor league contract to return to the Boston Red Sox. However, on April 1, 2011, he was released. On April 14, 2011, DiNardo signed with the Long Island Ducks of the independentAtlantic League of Professional Baseball. DiNardo signed a minor league contract with the Oakland Athletics on May 21, 2011. He played for the Double-A Midland RockHounds and with Triple-A Sacramento, making 19 appearances with a 5.61 ERA and 4–7 record. In 2012, DiNardo played in Taiwan for the Lamigo Monkeys of the Chinese Professional Baseball League. DiNardo played for the Lancaster Barnstormers of the independent Atlantic League in 2013, going 5–9 with a 5.25 ERA in 20 games. He tossed the franchise's first ever no-hitter on May 8, 2013, against the Long Island Ducks. He retired in August of that year.
