"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.
Cespedes connected for a two-run homer off Seattle reliever Shawn Kelley (0-1) to give Oakland a 2-1 lead in the bottom of the seventh. Josh Reddick followed with a solo shot off George Sherrill to give the A's a two-run cushion.
"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."
The A's opted not to re-sign Japanese slugger Hideki Matsui after a disappointing 2011 season and are hoping Cespedes can provide more production in the middle of the order.
The late rally Thursday was an encouraging sign for Oakland, which had only scored one run in the first 17 innings of the season.
Oakland manager Bob Melvin said Cespedes has been showing steady improvement since joining the team at the beginning of this month.
"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."
The 26-year-old Cespedes played in Cuba's top league for eight seasons before defecting in 2011. He starred for Cuba in the 2009 World Baseball Classic, hitting .458 with two home runs and five RBIs in six games.
Ichiro Suzuki, who was 4 for 5 in Seattle's 3-1 win over Oakland on Wednesday, was hitless in four at-bats Thursday.
Oakland starter Bartolo Colon picked up the win after striking out six and holding the Mariners to one run on three hits over eight innings. Grant Balfour pitched a scoreless ninth for the save.
"I mixed my pitches well," Colon said. "I tried to go inside with my two-seamer and outside with my fastball."
Jonny Gomes completed the scoring in the eighth with a solo homer off reliever Steve Delabar. Seattle scored its lone run on a solo homer by Dustin Smoak in the seventh.
Even though Suzuki was quiet at the plate he excited the crowd of 43,279 in the fifth inning with a fine leaping catch up against the wall in right to take away a base hit from Kurt Suzuki.
MLB and the players' association are using the 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."
The rest of the big league teams start on April 4, when the renamed Miami Marlins open their new ballpark against the World Series champion St. Louis Cardinals. In the meantime, the A's and Mariners will resume playing spring training games this weekend before facing each other in Oakland on April 6.