Cespedes saved his best for last, a 452-foot blast to the third deck above left field that officially measured as the longest of the night.
Athletics third base coach Mike Gallego again pitched to Cespedes, who went deep 32 times in last year's derby at Citi Field in New York. Gallego's arm looked nearly out of gas by the final round.
Cespedes topped Toronto's Jose Bautista, and Frazier surprisingly beat Miami's Giancarlo Stanton in the semifinals.
Bautista and Stanton each earned a bye to the semifinals under the new bracketed format, which gave each player seven outs and pitted the survivors from each side in the final round. Bautista went deep 10 times in the first round, keeping the fans in the second deck above left field on their toes, and Stanton hit six.
That was all, though.
After a long wait for his next turn, Stanton put up a zero in the semifinals and let Frazier advance with only one.
Oh, but Stanton's six were beauties.
One landed in the third deck above left field, about a half-dozen rows shy of the very top of the ballpark. Another reached the second deck above the center field batter's eye, a place never touched by a ball during an actual game here. Stanton has been credited with three of the 15 longest home runs in the majors this year, including the second-farthest at 484 feet.
Bautista, the AL captain, has 11 home runs in 14 regular-season games here, the most by any visiting player. That's only one less than Twins cornerstone Joe Mauer, who has played 284 career games at Target Field.
Cespedes, who beat Athletics teammate Josh Donaldson in a tiebreaker after each finished with three in the first round, breezed by Baltimore's Adam Jones in the second round. Frazier topped NL captain Troy Tulowitzki on the other side.
Colorado's Justin Morneau, the fan favorite after 10-plus years and four All-Star games for the host Twins, was eliminated in the first round.
Morneau returned to his roots, and so did the event itself, considering the inaugural contest was held at the Metrodome before the 1985 All-Star game. Admission then was a mere $2, slightly less than the $200-and-up price tags on the derby these days. The original form was actually a 1960s-era television show, featuring sluggers like Harmon Killebrew of the Twins.
R Oakland's Yoenis Cespedes hits 28 home runs, beating Cincinnati's Todd Frazier 9-1 in the final round.
• Cespedes also has the longest hit of the night, at 452 feet. • Cespedes is the first repeat winner since Ken Griffey Jr. in 1999.