Vargas worked two scoreless innings, giving up only a single to Tommy Medica. Vargas was signed as a free agent from the Angels, filling the rotation void left by Ervin Santana.
Vargas got help from left fielder Alex Gordon, who raced in to grab Everth Cabrera's game-opening line drive. Cabrera was in the Padres' lineup for the first time; he missed the first two games with flu.
"I felt fine, was able to throw all my pitches, was able to get acclimated to Salvy (catcher Salvador Perez) back there and we just kind of moved along," Vargas said.
Right-hander Ian Kennedy, obtained by the Padres at the Trade Deadline last year, also reeled off two scoreless innings in his first start. He gave up a double to Mike Moustakas, and a walk with two strikeouts.
Brad Penny, a veteran right-hander who didn't play last year, was touched for five hits and three runs in his two innings for the Royals, but got credit for the victory. Maybin cracked his homer off him in the third inning. It was Maybin's first home since last June 9 when his season ended because of injuries.
"Man, it felt good. I know it's only two games in, but it felt really good to kind of click one," Maybin said. "Just to kind of get that reassurance that the body feels well. You always gain confidence when you're able to put together a good at-bat."
Kennedy appreciated the blast.
"That was nice, I joked and said, 'He's back,'" Kennedy said. "That was a great swing, though. That was like the Cameron Maybin that I've seen hit some far balls against the D-backs, when I was with them."
The Royals scored four runs off right-hander Keyvius Sampson in the third on Gordon's two-run double and RBI singles by Eric Hosmer and Brett Hayes. They added three runs against righty Adys Portillo in the fourth, an inning launched by Justin Maxwell's double.
Royals closer Greg Holland pitched a scoreless inning, giving up only Medico's third straight single. Kelvin Herrera worked a perfect inning with two strikeouts.
Padres reliever Dale Thayer reeled off a perfect seventh with two strikeouts.
Up next: The Padres will play two Sunday, taking split squads to Goodyear, Ariz., to face the Reds and Glendale, Ariz., to meet the Dodgers. Both games are slated to begin at 12:05 p.m. PT. Projected to be in the rotation out of camp, Tyson Ross will get the start against Cincinnati with Matt Wisler, Burch Smith, Anthony Carter and Tony Sipp set to follow. Swing man Robbie Erlin will get the nod vs. Los Angeles. Listen to the Padres play the Reds on Gameday Audio or watch them take on the Dodgers on MLB.TV.