Backup catcher Wil Nieves hit his first career grand slam, a drive off former San Diego star Jake Peavy, and the Padres beat the San Francisco Giants 6-4 Sunday to take three of four against the defending World Series champions. It was the first career slam and just the 10th homer overall for the 37-year-old Nieves,who was a 47th-round draft pick of the Padres in 1995. He signed as a minor league free agent in January and won the backup job after Tim Federowicz, obtained from the Dodgers in the Matt Kemp deal, was sidelined following knee surgery. Peavy (0-1), whose first start of the season was delayed because of a back injury, loaded the bases on a single by Kemp, a walk to Justin Upton and a one-out single by Will Middlebrooks.