Beck made his Major League debut on May 6, 1991, against the Montreal Expos. His performance was forgettable (2.0 IP, 3 H, 2 ER), but his season numbers were more impressive. He had a 3.78 ERA, pitched innings in 31 games, and struck out 38 while walking 13. In , Beck took over as the regular closer from Dave Righetti and posted a record of 3–3 with 17 saves and a 1.76 ERA. He pitched 92 innings over 65 games and struck out 87 while walking only 15. In he recorded 48 saves, including 24 consecutive. At the time, both marks were Giants franchise records. Beck found success using a sinker, slider, and splitter.