Boston took a seemingly commanding 9-1 lead into the sixth, but the lopsided advantage morphed into a 15-9 slugfest victory over Kansas City at Fenway Park.
The offensive explosion, which included two home runs from Kevin Youkilis, backed the strongest outing of the season for Smoltz, who allowed one run on four hits over five frames to claim his first win since April 17, 2008 -- a span of 450 days.
"I've checked in, that's what I feel like," said Smoltz, who improved to 1-2 in four starts. "All kinds of thoughts come through my head. I haven't had a chance to smile after an outing yet, but today will make the All-Star break a lot more fun."
Smoltz's performance, which included a season-high seven strikeouts, almost went for naught, as the suddenly shaky Red Sox bullpen surrendered eight runs.
"It was back and forth," Youkilis said. "They were coming closer and closer. Fortunately, we got some distance in the end."
David Ortiz and Jason Varitek also homered for the Sox (53-34), who took a two-game lead over the Yankees in the American League East with New York's 14-8 loss to the Angels.
Ortiz's fourth-inning roundtripper marked the 1,000th hit of his career with Boston. He is the 30th player in club history to reach that plateau.
An early 9-0 deficit did nothing to discourage the Royals (37-50), who started to chip away with one run off Smoltz in the fifth before plating five more one inning later.
Kansas City could have had an even larger output in the sixth, had it not been for a fine play from J.D. Drew. With the bases loaded and one out, the right fielder played a one-hopper off the bat of Ryan Freel to perfection and threw out Miguel Olivo -- who had hesitated, thinking the ball might be caught -- at home plate.
"I thought I might have a play to catch the ball," Drew said. "Then I got caught in between, and it was one of those situations where instinct kicks in. I just wanted to catch and release as fast as I could. There really wasn't a chance for me to dive and catch, so I just ended up playing the hop nice, got it out of my glove quick, and threw a strike. It worked out well."
Following ineffective appearances from Justin Masterson, Manny Delcarmen and Hideki Okajima, who combined to allow six runs in one-plus inning after Smoltz departed, Daniel Bard was summoned to extinguish a two-on, no-outs threat in the seventh.
The 24-year-old rookie slowed the Royals' comeback bid, yielding two unearned runs on one hit while fanning three over two innings.
"It was fun," Bard said. "If you told me seven or eight years ago that I'd be helping John Smoltz get a win, I wouldn't have believed it. That was awesome."
"[Bard] threw a lot of strikes," manager Terry Francona said. "He pounded the zone at a time when we really needed that. We were getting that line moving a little too quick, and he settled everything down."
Bard's effort allowed the Red Sox to add much-needed insurance runs against a Kansas City bullpen that was not much better than Boston's. Royals relievers were tagged for seven runs on six hits in support of starter Gil Meche (4-9), who left the game in the fourth with a back spasm in his lower left side.
After Kansas City plated two runs in the top of the eighth to pull within three at 12-9, the Sox put the game away with a three-spot in the bottom of the frame.
Youkilis led off the inning with his second long ball of the night, followed by an RBI single from Aaron Bates -- the first hit of his Major League career -- and a Drew hit-by-pitch that forced in a run.
When the dust settled, Smoltz finally had a victory to his name.
"I'm thankful to the Red Sox organization for giving me a chance, to believe that I can do what I said I was going to do," Smoltz said. "I think the best is yet to come."
John Barone is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.