Maeda, who has expressed an interest in pitching in the major leagues, gave up two hits while striking out two and walking two before a crowd of 33,000 at Kyocera Dome.
The only hits given up by Maeda were a single to Robinson Cano in the first inning and a double by Dexter Fowler in the fifth.
"I am happy to finish my outing with a good result, especially in the first game of the series," said Maeda, who threw 71 pitches and got the win. "They made me throw a few more pitches than I wanted in the first inning but I got my rhythm after that."
Japan took a 1-0 lead in the second inning when Seiichi Uchikawa scored from third on a sacrifice fly by Nobuhiro Matsuda. Tetsuto Yamada drove in another run in the fourth with a line drive single to left, allowing Matsuda to score from second.
The MLB All-Stars beat a Japan split-squad team 8-7 in a warmup game on Tuesday but faced a stiffer challenge in the series opener.
"It was very good pitching on their part tonight," MLB manager John Farrell said. "We got an opportunity in the first with a couple of men on but Maeda really settled in and pitched effectively with an assortment of pitches for strikes."
The series marks the first time since 2006 that a MLB All-Star team has visited Japan.
Shohei Otani retired the side in order in the eighth. The 20-year-old right-hander is scheduled to pitch Game 5 before his home fans at Sapporo Dome.
"To see a guy at his age throw nearly 100 mph is impressive," Farrell said. "In one inning of work it seemed like he had a lot of poise. He has a long, loose body with tremendous arm speed."
MLB starter Matt Shoemaker took the loss after giving up both runs over six innings.
Los Angeles Angels first baseman Albert Pujols, Washington outfielder Bryce Harper and Baltimore outfielder Adam Jones withdrew because of personal and family commitments, the Major League Baseball Players Association said.
The five-game series also includes games at Tokyo Dome and Cellular Stadium in Okinawa.Suggest a correction