SAN FRANCISCO — Rafael Devers homered twice and drove in four runs as the San Francisco Giants beat the Atlanta Braves 5-0 on Saturday night behind Logan Webb’s magnificent pitching.Webb allowed one hit and struck out six in seven innings as the Giants (34-48) avoided falling 16 games under .500 for the first time since 2018. Mauricio Dubón’s one-out double in the second was his only blemish.Devers, a three-time All-Star who drew national criticism when he balked at leaving for a pinch-runner against Miami last Sunday, hit a solo homer off starter Bryce Elder in the second inning and a three-run drive in the third, giving him 800 career RBIs.Webb (5-5) walked two and retired the final 16 batters he faced, improving to 5-1 against the Braves. The right-hander has often pitched in hard luck this season, receiving no more than two runs of support seven times in 14 starts. Ryan Walker and Sam Hentges each retired three batters to complete the one-hitter.Devers crushed a 2-2 fastball from Elder in the second. Bryce Eldridge added a one-out double and scored on Drew Gilbert’s sacrifice fly to make it 2-0.Luis Arraez and Casey Schmitt hit consecutive singles to begin the third before Devers launched his 14th home run this …