The offseason proved very difficult for Ortiz, as on New Year's Day 2002, his mother died following a car accident. Gardenhire reached out and helped Ortiz deal with the death, and Ortiz prepared hard for the coming baseball season, both saddened his mother never saw him play at his best and determined to reach new heights. When the season began, Ortiz battled knee injuries. It was a tale of two seasons for Ortiz, as his .240 average with 5 homers and 33 RBI before the All-Star break was disappointing. But after the All-Star break, Ortiz quietly turned in one of the better second halves in baseball, batting .297 with 15 home runs and 42 RBI. On August 16, he hit a memorable home run off his friend Pedro Martínez at the Hubert H. Humphrey Metrodome, hitting an inside cut fastball into the upper deck. On September 25, he hit the first walk-off home run of his career, against the Cleveland Indians. He finished the 2002 season batting .272 with 20 home runs and 75 RBI. At this point in his career, the home run and RBI totals were both career bests. However, as he batted only .203 against left-handed pitching, Ortiz still was not always guaranteed to start if a tough lefty would be on the mound. His career year coincided with the Twins qualifying for the postseason, as the team won 94 games and upset the Oakland Athletics in the Division Series before falling in the 2002 American League Championship Series to the eventual World Series winning Anaheim Angels. Ortiz batted .276 in his first postseason, with 4 RBI. His 9th inning double in the decisive Game 5 of the Division Series put the Twins ahead 5–1 in a game they would hold on to win 5–4. The series-winning RBI was the first of what would be many clutch postseason hits in Ortiz's career.
After his release from the Twins, Ortiz had a chance encounter with Pedro Martínez at a restaurant in the Dominican Republic, and Martinez remembered a home run he had given up to Ortiz in August 2002. Excited at the prospect of his friend joining him on the Boston Red Sox (who needed a first baseman), Pedro began calling several Red Sox team officials to request that the team sign Ortiz. On January 22, Ortiz signed a non-guaranteed free agent contract with the Red Sox that would be worth $1.25 million if he made the team. New Red Sox General Manager Theo Epstein envisioned Ortiz as one of several candidates to fill a void at first base. Sabermetrics favorite Jeremy Giambi was widely expected to get most of the playing time, but also in the mix were primary third baseman Bill Mueller (who figured to DH at times), Shea Hillenbrand (who could play third base, first base, or DH), and Kevin Millar (who could play first base or outfield). The team's best hitter, outfielder Manny Ramirez, figured to DH at times also. When the season started, all of them made the team, including Ortiz, with the new designated hitter/first baseman taking player number 34 in honor of his mentor and friend on the Twins, Kirby Puckett.
Each time Ortiz crossed the plate after hitting a home run, he would look up and point both index fingers to the sky in tribute to his mother, Angela Rosa Arias, who died in a car crash in January 2002 at the age of 46. Ortiz also has a tattoo of his mother on his biceps.