His effort helped San Diego record its eighth straight win.
Geer (1-1) threw 107 pitches, did not walk a batter and struck out seven.
Reliever Edward Mujica worked the ninth to earn his first career save.
Brian Giles led San Diego with a two-run double in the fourth inning. Chris Burke hit a seventh-inning RBI single, one of just five hits for the Padres.
San Diego last won eight straight during a nine-game winning streak from April 30-May 8, 2006.
Chicago's run scored on Derek Lee's second-inning homer. Both he and Mike Fontenot had two hits for the Cubs, who have lost six in a row.
Losing pitcher Randy Wells (0-1) surrendered three earned runs and five hits in seven innings with a walk and seven strikeouts.
Copyright 2009 by United Press International.