Doing so in 154 games, the Giants have reached 100 wins in their fewest games in the live-ball era (since 1920). It's the first time they have been the first team in MLB with 100 wins since moving to San Francisco in 1958.
San Francisco leads theLos Angeles Dodgersby 1 game. The Giants have won 16 of 21.
Kervin Castro (1-0) tossed two innings for his first major league victory, and the Giants reached 100 wins for the first time since going 100-62 in 2003.
"It's a big accomplishment, but we're looking for more," San Francisco pitcherAlex Woodsaid.
The Giants haven't won the NL West since 2012, when they captured the second of three World Series titles in a five-year span. Coming into the season, they were lightly regarded with the Dodgers andSan Diego Padresgetting most of the attention but have surprised many.
"It's a big deal," manager Gabe Kapler said of winning 100 games. "We know our division is extraordinarily talented, but we also know that we're talented. Our goal was to win the division and not just sneak into the playoffs."
San Francisco blew the game open in the seventh. Yastrzemski followed singles by Brandon Crawford and Evan Longoria with his 25th homer off reliever Ashton Goudeau (1-1). The Giants tacked on another run onBuster Posey's RBI single.
Tommy La Stella, Crawford and Brandon Belt had solo home runs to give San Francisco a 3-2 lead after six. La Stella and Crawford had three hits each, and Belt finished with two.
San Francisco has 234 home runs, one fewer than the club record set in 2001 when Barry Bonds hit 73. The Giants lead the NL in homers and are second in the majors toToronto's 241 despite not having a player hit more than 27 this season.
Three players -- Belt, Crawford and Yastrzemski -- have 22 or more, and seven other players have reached double digits in home runs.
"So many of the home runs have been meaningful," Kapler said. "I can't help but think of the ones that changed a game for us. We're getting contributions from everyone on our roster."
ESPN Stats & Information and The Associated Press contributed to this report.
Giants rip 4 homers in 100th win of season
Tommy La Stella, Brandon Crawford, Brandon Belt and Mike Yastrzemski combine for four home runs as the Giants go on to win 7-2 over the Rockies.