The Red Sox clinched the American League championship series in six games, setting up a World Series rematch with the St Louis Cardinals.
They will host game one on Wednesday against the team they swept in 2004 to end their 86-year title drought.
The Cardinals won the National League title pennant on Friday by eliminating the Los Angeles Dodgers in six games.
With 21-game winner Max Scherzer on the mound, Detroit took a 2-1 lead in the sixth inning and held it until Boston loaded the bases on a double, a walk and an error by shortstop Jose Iglesias.
Victorino lofted an 0-2 pitch from Jose Veras over the Green Monster to set off a celebration in the Red Sox dugout and in the Fenway Park stands.
Junichi Tazawa got one out for the win, Craig Breslow pitched a scoreless eighth and Koji Uehara got the last three outs before the Red Sox poured out of the dugout to begin their now-familiar celebration on the mound.
It's the 13th AL pennant for the Red Sox and their first since 2007, when they swept the Colorado Rockies to win it all for the second time in four seasons.
Boston swept the Cardinals in '04, winning game four in St Louis to clinch the title that put an end to generations of disappointment.
The latest trip comes one year after a last-place finish that forced the team to jettison its high-priced stars, rebuild the roster and bring in manager John Farrell.
Victorino was one of the biggest additions, and he delivered on Saturday as he did for much of the season.
Scherzer got one out in the seventh but left after walking rookie Xander Bogaerts to put runners on first and second.
Drew Smyly got Jacoby Ellsbury to hit a grounder up the middle, but it popped out of Iglesias' glove behind second base and everyone was safe.
Veras came in and quickly got ahead of Victorino. But he hung a curveball and Victorino sent it toward the 37-foot left-field wall, which had already knocked down two Red Sox line drives.
This one left no doubt.
It was the second career post-season grand slam for Victorino, who also had a record-setting hit-by-pitch in the sixth.