taschner was drafted again, this time by the san francisco giants in the second round of the 1999 major league baseball draft. the giants assigned him to their short season a-level minor league affiliate, the salem-keizer volcanoes of the northwest league. taschner earned a 3–2 record in the latter half of 1999, striking out 36 batters in 29 innings. he injured his shoulder in his last outing for salem-keizer. after surgery he sat out all but one month of the 2000 season for the san jose giants. he returned to san jose in 2001 where he pitched 2 1/2 months making the california league all-star team. unable to pitch in the game or the rest of the season he had surgery again, this time on his left elbow. between the two years, taschner posted a 6–6 record in 24 games (16 starts), striking out 94 batters in two years while pitching a total of 88 innings. however, he hit another setback in 2002, as he missed the entire season recovering from tommy john surgery. the road to recovery was not easy for taschner, as his record with the norwich navigators in 2003 was 0–6; he posted an era of 5.68, the highest of his minor league career to date, striking out only 46 batters and allowing 48 earned runs. taschner's 3–1 record with norwich in 2004 was enough to earn him a promotion to the aaa fresno grizzlies, where he had a 4–7 record. taschner remained at fresno to begin the 2005 season, but he began to work exclusively as a relief pitcher and regained the form of his early career, posting a 3–0 record and a 1.64 era before being called up to the major leagues for the first time. taschner was first called up to the giants on june 12, 2005. in his first season, he made 24 appearances as a reliever, notching a 2–0 record with 19 strikeouts and a 1.59 era. taschner earned his first major league win on august 30 against the colorado rockies when the giants rallied for a comeback win in the ninth inning. in 2006, he made the opening day roster, but was sent back to the minor leagues after posting a 34.71 era in 2⅓ innings; he posted a 6–7 record with fresno and struck out 68 batters in 49⅓ innings. he spent more time with the giants throughout the season as well, making 24 appearances and posting no wins with an 8.38 era in the major leagues.