Middlebrooks had three hits and Upton had two.
"When we're all on it, it's a scary lineup," Middlebrooks said. "When a couple guys are on it, it's a scary lineup."
Kemp and Middlebrooks were both 3 for 3. The Padres were last in the majors last year in batting average (.226) and runs (553).
"This year, we'll be able to produce some runs and get some things going for these arms that we have," Kemp said.
"Hopefully, we can all get in sync . hit a lot of home runs and drive in a lot of runs. That would be a lot of fun."
Upton, who went 2-for-3, singled in a run in the fourth.
"We have a lot of interchangeable pieces, too," Upton said.
"It will be fun to be a part of. A lot of talent. We just got to put it in motion."
Casey McGehee went 2 for 3 for the Giants.
"I'm glad we're not starting the season," said Giants manager Bruce Bochy. "We're not ready. We're getting our guys ready to go. We got some work to do."
Giants: Petit gave up four runs and four hits in two-plus innings while walking three.
"Petit got a little tired and started making some mistakes," Bochy said. "Early, he was really sharp."
Padres: Kennedy allowed three runs and five hits in 1 2-3 innings, while striking out two.
Despite the brief stint, Kennedy threw 50 pitches, thanks to foul balls and deep counts by hitters such as the Giants' Nori Aoki.
"He's a pesky hitter," Kennedy said. "Please, put it in play somewhere."
HOPING FOR BOUNCE BACK:
The Padres are hoping for a better season from Jedd Gyorko, who slumped along with much of their lineup last year.
"I think what happened was (pitchers) made adjustments to Jedd, and Jedd didn't adjust fast enough," manager Bud Black said of Gyorko, who hit .210 with 10 homers and 53 RBIs.
"The major league pitcher exploited Jedd's aggressiveness. Jedd wants to hit. When you think you can hit, you swing. Jedd expanded his zone a little bit and swung at pitches out of the strike zone."
In addition, the Padres probably "unfairly put a lot of pressure" on Gyorko by hitting him in the middle of the order, Black said. This year, Kemp and Upton can be there.
"The way we started offensively last year, a lot of guys had the mentality that they wanted to be the guy," Black said. "We were scuffling and to a man I think they all tried to do too much. When that happens, usually the results don't go your way."
Giants: Sergio Romo, who has been bothered by a sore shoulder, threw his first bullpen session Tuesday. If there are no ill effects, Romo soon should be ready for Cactus League games, Bochy said. "It's up to Serg," the manager said.
Padres: Tim Federowicz, expected to be the Padres' backup catcher, is set to undergo surgery Thursday to repair a tear in the lateral meniscus of his right knee. The extent of the damage and his projected return won't be known until afterward.
Giants: Tim Hudson will start at home Wednesday vs. Milwaukee.
Padres: Brandon Morrow is expected to start Wednesday at Kansas City.