Marlins manager Mike Redmond is scratching his head, too.
"They've been able to hit his fastball," Redmond said. "They take advantage of any mistake that he seems to make. I don't know if they've got something on him, but they've been able to do quite a bit of damage."
Coming out of the All-Star break, it was more of the same for the Marlins. They've lost five games in a row and 21 of their past 31, and they're seven games under .500 for the first time.
"It wasn't what we had drawn up coming back from the break," third baseman Casey McGehee said. "We need to pick it up really quick."
The Giants are hitting again, which is why they're back in first place in the NL West. They totaled 13 hits, and All-Star Madison Bumgarner (11-7) took advantage of the support, allowing one run in six innings.
"Good to see everybody playing like that," Bumgarner said. "I guess everybody had a good All-Star break."
The Giants began the night averaging less than three runs per game in July, worst in the majors, but they've totaled 17 runs in their past two games. Those wins came after an 11-22 stretch that cost them first place.
"This is who we were the first 60-plus games," manager Bruce Bochy said. "Then we turned into a different team."
San Francisco led 9-0 before Miami's Giancarlo Stanton hit his 22nd home run, most in the NL. His drive passed the home-run sculpture and caromed off the backdrop beyond the center-field wall.
"It was a pretty good pitch, I thought," Bumgarner said. "But everyone knows how far he can hit the ball."
Brandon Crawford set the tone for the Giants, hitting the 11th pitch he saw for a two-run homer in the second inning.
"To have a good at-bat early in the game and get us on the board felt really good," he said.
Sandoval hit his 12th homer to end Eovaldi's night in the Giants' five-run fifth.
Buster Posey and Michael Morse each had three of San Francisco's 13 hits. The Giants scored their first four runs with two outs and went 6 for 11 with runners in scoring position.
Bumgarner lowered his ERA to 3.38 but also struck out three times to drop his batting average to .256.
"I'll trade the not hitting very good for pitching good any day," he said.
Crawford's eighth homer put the Giants ahead 2-0. They added two more runs in the third on two-out RBI singles by Posey and Morse.
Hunter Pence and Morse each doubled and scored in the fifth.
Notes: Before the game, the Marlins placed RHP Kevin Gregg on the 15-day disabled list retroactive to Monday with right elbow inflammation. RHP A.J. Ramos (right shoulder) was reinstated from the disabled list. ... RHP Jacob Turner will rejoin the Marlins' rotation and start Tuesday at Atlanta. He's 2-6 with a 6.22 ERA in 17 games. ... RHP Tim Hudson (7-6, 2.87), who has lost his past four decisions, is scheduled to start Saturday for the Giants against RHP Henderson Alvarez (6-4, 2.63).