MILWAUKEE (AP) -- Stephen Strasburg's fastball was on, but the changeup was off.
Minus one pitch in his arsenal, the Washington Nationals ace got shelled for one of the worst outings of his career.
Scooter Gennett had a grand slam and five RBIs, Khris Davis added a solo shot and the Milwaukee Brewers roughed up Strasburg in a 9-2 victory Wednesday.
Strasburg (6-6) was tagged for eight hits and seven runs in 4 2-3 innings. Strasburg also allowed seven earned runs in a two-inning start on July 12, 2013, in an 8-3 loss to Miami.
Strasburg said he was having issues with his mechanics that were causing hitters "to see the ball a lot better. ... Still trying to figure that out. It just doesn't feel the same, it doesn't look the same."
Manager Matt Williams said Strasburg was commanding his fastball, but the changeup threw him off. That's not good news against the aggressive Brewers, even with top hitters Ryan Braun, Jonathan Lucroy and Aramis Ramirez all getting a day off.
"So he couldn't go to it, he was missing with that," Williams said. "And then he got behind in the count and they took advantage of it. This team swings at fastballs and they hit them. If you get behind, you can get in trouble."
Homer-prone starter Marco Estrada (7-4) allowed just two hits and pitched effectively into the seventh for the Brewers, who bounced back a day after falling 4-2 in 16 innings to Washington.
Estrada has given up a major league-high 24 homers, but didn't allow a homer Wednesday.
Estrada's only other outing without a homer was during a 6-1 loss to St. Louis on April 15. On Wednesday, fans showered him with a standing ovation after he got lifted in the seventh.
"The way the game was going, I'm sure everyone was really excited about it - but to get some cheers in that game, it made me feel really good," Estrada said.
Gennett turned on a 2-1 fastball for his first career grand slam and fifth homer of the season that landed on the concourse above right-center field in the second for a 4-1 lead.
Davis opened the bottom of the fourth with a no doubt-about-it shot above the "Goodwill" sign in left-center for his team-high 14th homer to make it 5-2. Davis swung at a first-pitch fastball.
"A guy like Strasburg, you don't want to get to two strikes off him," Davis said. "You want be aggressive and get him early."
The Brewers' bats broke out after scoring just two runs in 25 innings in the first two games of a series between NL division leaders. Rookie Taylor Hill, making his major-league debut, allowed two runs and five hits in 3 1/3 innings of relief.
The benches did empty briefly after Carlos Gomez slid through second base on second baseman's Kevin Frandsen's relay on a double play to end the eighth inning. Gomez had reached after getting hit by a pitch.
Shortstop Ian Desmond took issue with the slide and exchanged words with Gomez. No punches were thrown and the teams returned to their dugouts.
"I respect the way he plays the game, but I got no respect for that," Desmond said. "In a World Series game, you slide like that. In a seven-run differential game, there's no time for that. If you're going to defend that, I've got no respect if you can defend that."
Manager Ron Roenicke said it was a hard but clean slide.
"You get hit with a ball, you get a little adrenaline going, and you're going to go in hard," the skipper said.
NOTES: Nationals OF Bryce Harper (left thumb) has joined Class AA Harrisburg for the next phase of his rehab stint for a left thumb injury. ... Williams said C Wilson Ramos (right hamstring) could rejoin the team in time for the start of Thursday's four game series in Chicago against the Cubs. ... Doug Fister (6-5) will start the opener of the Cubs series for Washington. Milwaukee opens a four-game set on Thursday at Miller Park with Wily Peralta (8-5) taking the hill.