Clayton Kershaw bolstered his case for the Cy Young Award with his 20th victory as the Los Angeles Dodgers beat visiting San Francisco 2-1 on Tuesday and dealt a crucial blow to the Giants’ postseason hopes.

The Dodgers snapped San Francisco’s season-high eight-game winning streak and dropped the Giants 4 1/2 games behind Atlanta in the National League wild card race.

San Francisco, which is 5 1/2 behind Arizona in the NL West, has eight games remaining, including three against the Diamondbacks this weekend.

Kershaw (20-5) gave up one run and struck out six over 7 1/3 innings to become the Dodgers’ first 20-game winner since Ramon Martinez in 1990.

Chris Stewart homered in the eighth inning off Kershaw, who recorded his third win over Giants starter Tim Lincecum (13-13) this season.

Kershaw improved to 7-0 in his last eight outings and won his eighth straight start at Dodger Stadium. Javy Guerra worked around Mark DeRosa’s leadoff single in the ninth for his 19th save.