Gardenhire got even more than he expected.
Stewart hit his first career homer in the first inning, hit another home run in the second inning and drew a bases-loaded walk in the seventh as the Tigers beat the Kansas City Royals 11-8 on Thursday night.
"The ball was flying out in BP, especially when he was hitting them, so I had a feeling he might have a big night," Gardenhire said. "What he did tonight is the reason he's considered one of our top prospects."
Stewart, a September call-up playing in his 11th game, became the first Tigers rookie to drive in six runs in a game since Ryan Raburn had seven against the Chicago White Sox on July 25, 2007.
"I felt great before the game, but there are days you have a great BP and a terrible game, so I didn't want to get too confident," he said. "It was an awesome feeling, though."
Six Tigers had at least two hits and Detroit snapped a seven-game home losing streak.
Kansas City lost its fifth straight despite hitting three doubles and four homers.
"We swung the bats well," Royals manager Ned Yost said. "We just didn't pitch well."
The Tigers led 9-5 after two innings as the teams combined for five home runs, six doubles, a triple and a double steal. By that point, both starting pitchers were gone.
Detroit's Matthew Boyd allowed five runs while getting four outs.
"Gardy definitely made the right move getting me out of there," Boyd said. "I just didn't have anything out there."
Kansas City's Jorge Lopez (2-5) gave up seven runs without getting an out in the second.
"I was up from the first pitch I threw," he said. "The plan was to keep the ball down, but I couldn't make pitches."
Zac Reininger (1-0), the second of seven Detroit pitchers, picked up his first major-league victory.
Jorge Bonifacio gave the Royals the lead with a three-run homer off Boyd in the first, but the Tigers came back with four in the bottom of the inning. Stewart hit a two-run homer just over the right-field fence and Nicholas Castellanos hit the next pitch to nearly the same spot.
Grayson Greiner made it 4-3 with a sacrifice fly later in the inning, and the runs kept coming in the second. Brian Goodwin gave the Royals a 5-4 lead with a two-run homer in the top of the inning, but Stewart made it five RBI in two innings with a long three-run home run in the Tigers' second.
"I was running to first and praying on the first one because I didn't know if it was going to get out," said Stewart, who has 83 minor-league homers in the last three seasons. "The second one, I knew it was gone."
Glenn Sparkman replaced Lopez and gave up a triple to Castellanos and Victor Martinez's RBI double before getting the first out of the second inning. Greiner picked up his second RBI with a two-out single, giving the Tigers a 9-5 lead.
Hunter Dozier hit a two-run homer off Reininger in the fourth, pulling the Royals within 9-7, but the next four relievers combined for 4 1/3 scoreless innings as Detroit maintained the lead into the ninth inning.
"We didn't want to use that many arms in the first game of a four-game series, but they did the job," Gardenhire said.
Stewart walked with the bases loaded in the seventh for his sixth RBI.
V-MART KEEPS HIS RECORD
In the first inning, Victor Martinez lined a ball into the right-center field gap -- the perfect place for a triple at spacious Comerica Park -- but his lack of speed turned it into a double. With nine games left in his final season, Martinez has 3,937 plate appearances for the Tigers without hitting a triple, the most in franchise history. Aaron Robinson is second with 868.
STEWART'S BIG DAY
Stewart came within inches of an even more memorable game. In the seventh, with the bases loaded and a 3-2 count, he lined a Brandon Maurer slider into the right-field corner for what looked like a bases-clearing double.
That would have tied Harry Heilmann and Jim Northrup's franchise record of eight RBI in a game, but the ball sliced just foul. He drew the bases-loaded walk on the next pitch.
"That was a great at-bat," Gardenhire said. "He got a 3-2 pitch he could drive, then came right back and had the patience to take the walk."
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