The Cuban defector's go-ahead, two-run drive in the seventh inning off reliever Shawn Kelly sent the A's on to a 4-1 victory Thursday night at the Tokyo Dome.
"I wake up early every day and get to the field early and work hard because the baseball is different than in Cuba," Cespedes said through a translator.
Bartolo Colon (1-0) won his Oakland debut after spending last season with the Yankees, pitching three-hit ball over eight innings and allowing his only run on Justin Smoak's seventh-inning homer.
"We couldn't get guys on base," Smoak said. "He threw the ball well tonight."
Josh Reddick followed Cespedes and homered off George Sherrill to give Oakland back-to-back homers. Jonny Gomes hit his first Oakland home run in the eighth off Steve Delabar, and Grant Balfour pitched a 1-2-3 ninth for the save, his first since becoming the A's closer.
A day after getting four hits in Seattle's 3-1 win, Japanese star Ichiro Suzuki went 0 for 4 for the Mariners. He excited the crowd of 43,279 in the fifth with a leaping catch up against the wall in right to take away a base hit from Kurt Suzuki.
Kelley (0-1) lost in relief of Jason Vargas, who given a lead walked Coco Crisp leading off the seventh.
"With the matchups we had we felt that was the right time to get him out of there," Seattle manager Eric Wedge said. "He had been through the lineup a couple of times, so we felt it was the right move. Kelley just hung a slider to Cespedes."
Both teams now head back to U.S., with the Mariners resuming spring training games in Arizona on Saturday and Oakland playing exhibition games in the Bay Area. They go back to games that count on April 6, when the Mariners start a two-game series at the A's that is followed by a rare Sunday day off.
Other big league teams start play April 4, when the renamed Miami Marlins open their new ballpark against the World Series champion St. Louis Cardinals.
Cespedes, who hit .458 with two homers and five RBIs for Cuba at the 2009 World Baseball Classic, defected from Cuba last summer and agreed in February to a $36 million, four-year contract with the A's.
He went 1 for 3 with a double against Felix Hernandez and two strikeouts in his big league debut. A day later, Cespedes moved up one notch to sixth in the batting order and was 1 for 3 with one whiff.
"They tried to throw me sliders every at-bat, so I had to adjust to hit the ball," Cespedes said. "It was great to hit a home run here for the Japanese fans."
Oakland manager Bob Melvin said Cespedes has been showing steady improvement.
"He's getting more and more comfortable every day," Melvin said. "The challenges he faces on the field are probably the easiest for him. He's been dropped into a situation that is difficult both on and off the field."
Colon, the 2005 AL Cy Young Award winner, started 8-6 for the Yankees last year before slumping to an 0-4 record in his final 10 starts. The 38-year-old, Oakland's oldest starting pitcher since 41-year-old Tom Candiotti in 1999, struck out six and walked one.
"I mixed my pitches well," Colon said. "I tried to go inside with my two-seamer and outside with my fastball."
Vargas allowed one run and two hits in 6 1-3 innings, quite a turnabout from spring training, where he had a 12.46 ERA in three starts. After Crisp's walk opening the seventh, Gomes flied out and Wedge removed Vargas after 85 pitches.
Kelley got Kurt Suzuki to bounce into a forceout for the second out. After Cespedes homered. Sherrill came in, and four pitches later Reddick connected for a 3-1 lead.
"We didn't execute pitches," Wedge said. "We were one pitch away from being through that inning."
MLB and the players' association used series to assist rebuilding in Japan following last year's earthquake and tsunami. A group of players and coaches traveled to the disaster zone on Tuesday to conduct a baseball clinic.
"The main reason we came here was because of the tsunami," Melvin said. "I know MLB has been coming every four years, but the tsunami made this trip happen for sure."
NOTES: Oakland had scored one run in 17 innings before Cespedes' homer. ... While the A's have lost eight straight openers, they've won six of their last eight Game 2s. ... Oakland also split its 2008 opening series in Japan against Boston. ... With 17 opening-day hits for the Mariners, Suzuki moved three ahead of Ken Griffey Jr. for the most in team history.