Upton slugged a first-inning grand slam and added a two-run double in a four-run second inning off losing Dodgers starter Carlos Frias, whose ERA more than doubled from 2.55 to 5.34. Will Middlebrooks hit a solo homer and Derek Norris also drove in two runs off Frias, who allowed 12 hits with no strikeouts in four-plus innings.
Shields, who allowed a two-run homer to Alex Guerrero in a three-run seventh inning, became the first Padres starting pitcher to begin a season with a 6-0 mark since Andy Hawkins went 11-0 to begin the 1985 season.
MOMENTS THAT MATTERED Trouble comes early: In six previous starts this season (Major and Minor Leagues), Frias hadn't allowed four runs in a game, but he was four runs down after four hitters in this game because of Upton's slam. It was the second home run he's allowed this season. Through two innings Frias had allowed eight runs, one more than he allowed in his other six Dodgers games this year. More >
"I struggled with my pitch command," said Frias.
A grand (slam) time: Upton's grand slam off Frias in the first inning was the fourth of his career -- and the third against the Dodgers. His previous grand slams against Los Angeles came on May 17, 2013 (off Paco Rodriguez) and June 2, 2009 (off Randy Wolf) while Upton was with the D-backs. More >
"I don't think we cared how we got our runs today, but it was nice to get some runners in scoring position, bases loaded, and get some hits in that situation," Upton said.
A fast start for Shields, too: It wasn't just the Padres' offense that got off to a fast start Sunday. Shields wasn't tested much early as he got a lot of ground balls and worked fast and efficiently with a big lead. He retired 16 of 17 at one point but loaded the bases with no outs in the seventh. That's when he got Andre Ethier to bounce into a double play before allowing the home run to Guerrero. More >
Playing all the hits: The Padres finished with 20 hits, which ties their season-high. Every starting player -- even Shields -- had at least one hit and Abraham Almonte came off the bench to knock in the 11th run of the game with a single in the eighth inning.
"He's been taking the boys and putting us on his back, for sure. We're going to need some of the other guys to step up as well, to win more ball games, but he's been phenomenal. He's an All-Star caliber player and doing his job," -- Shields on Upton
SOUND SMART WITH YOUR FRIENDS
Frias became the sixth Los Angeles Dodgers pitcher to allow 10 runs in a game, the last being Brad Penny in 2008. Also in that dubious club are Tom Candiotti, Chan Ho Park, Odalis Perez and Carlos Perez.
The Dodgers lost a manager's challenge in the top of the ninth inning when Will Venable was ruled safe at first base by umpire Jeff Kellogg, who ruled Venable beat Guerrero's throw. A replay official ruled the call stands.
MORE QUALITY STARTS
Shields' quality start on Sunday was the sixth consecutive of its kind for the Padres, which is a season-high. Before this streak started -- Shields has two of the quality starts in this stretch -- the team didn't have consecutive quality starts since April 14-15.
WHAT'S NEXT Padres: The Padres head to Anaheim for the first of three games against the Angels at 6:05 p.m. PT on Monday, their first trip there since 2009. Tyson Ross gets the start. Ross hasn't allowed more than three runs in any of his last four outings.
Dodgers:Brett Anderson will start for the Dodgers at 5:10 p.m. PT, hoping it doesn't rain, which it has in his last three starts in Los Angeles, Denver and San Francisco. This will be the first time he's faced the Braves.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter and listen to his podcast. Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.