Early years: 1997–1999 Matsunaka made his debut at the
ichigun (Japanese equivalent of "major league") level in , his
rookie season, as the starting first baseman and
No. 7 hitter in a
regular season game against the
Seibu Lions on May 31. His first
home run came more than a year later against Lions
right-hander Fumiya Nishiguchi on September 5 . Matsunaka became the Hawks' starting first baseman in with the departure of
Luis Lopez, hitting .268 with 23 home runs and 71
RBI and leading them to their first championship in 35 years as they won the league title as well as that year's
Japan Series in five games over the
Chunichi Dragons. His 23 homers were second to only
Hiroki Kokubo on the Hawks.
2000–2002 Matsunaka had a breakout year in , hitting .312 with 33 homers and 106 RBI and winning the
Pacific League Most Valuable Player award for the first time in his career. However, while the Hawks won the league title and reached the
Japan Series for the second straight year, they blew a commanding 2-0 lead to the
Yomiuri Giants and lost in six games. Matsunaka was a factor in this loss, going just 1-for-20 with one home run in the series. Matsunaka put up his second consecutive .300-30-100 season the following season , hitting .334 with 36 home runs and 122 RBI. The Hawks had a particularly potent
lineup that year, with Matsunaka, Kokubo (44), catcher
Kenji Johjima (31), and second baseman
Tadahito Iguchi (30) all hitting 30 or more home runs. It marked the first time four players on the same team had ever hit 30 or more homers in the Pacific League, and the four were dubbed the "30-Homer Quartet". However, while the Hawks broke a franchise record by hitting 203 home runs as a team, they finished second to the
Osaka Kintetsu Buffaloes in the pennant race, missing their third straight league title. Matsunaka struggled to adjust to the new
strike zone that the NPB had decided to implement in the season, hitting a career-low .260 with 28 home runs. He hit his 100th career home run on May 3 off
left-hander Itsuki Shoda in a game against the
Nippon Ham Fighters.
2003 In , Matsunaka bounced back from a disappointing previous year and hit .324 with 30 home runs and 123 RBI in the regular season, overtaking his teammate Johjima in RBI in the last game of the season to lead the league in that category for the first time. He led the Hawks to another pennant win and their first
Japan Series championship in four years over the
Hanshin Tigers. Despite the absence of Kokubo, their longtime
cleanup hitter, the Hawks collectively hit .297 (the highest team
batting average in NPB history), with four hitters putting up 100 or more RBI (the "100-RBI Quartet").
2004 The season was the finest of Matsunaka's eight-year
professional career. He hit .358 with 44 home runs and 120 RBI, becoming the first player in Japanese professional baseball since
Hiromitsu Ochiai (then of the
Lotte Orions) in to lead the league in batting average, home runs and RBI in the same season (he was tied with
Fernando Seguignol in home runs) and thus win Triple Crown honors. Making the feat even more impressive was that Matsunaka also led the league in
hits,
on-base percentage,
runs scored and
total bases, becoming just the second player in NPB history to lead the league in the aforementioned seven categories. Following the season, Matsunaka was rewarded with the second MVP award of his career as well as the
Best Nine and Golden Glove awards. However, while he led his team to the
playoffs, the Hawks fell in five games to the Lions due in large part to an abysmal showing by Matsunaka, who went just 2-for-16 in five games in the series.
2005 In , the following year, Matsunaka became the Hawks' everyday
designated hitter due to recurring problems with his
knees. He hit his 200th career home run against
Chiba Lotte Marines submariner Shunsuke Watanabe on April 17 and finished the year with a .315 batting average, 46 home runs and 121 RBI, leading the league in home runs and RBI for the second straight season and becoming the first hitter in NPB history to record more than 120 RBI in three straight seasons. However, the Hawks suffered yet another early playoff exit, this time falling in five games to the Marines. Again, Matsunaka faced most of the blame for the loss, hitting just 1-for-19 in the series. He signed a seven-year contract with the Hawks in the 2005
off-season, virtually ensuring that he would finish his career with the team.
2006 Coming off a triumphant victory in the inaugural
World Baseball Classic, Matsunaka hit .324 during the 2006 regular season and won his second
batting title that year, but his power fell substantially as he managed to hit only 19 home runs with 76 RBI. It was during this season that he began to see significant playing time in the
outfield, frequently seeing starts at
left field from interleague play onwards. The Hawks finished third in the regular season, defeating the Lions in the first round of the playoffs but ultimately being swept by the
Hokkaido Nippon Ham Fighters in the second round (though Matsunaka went 7-for-18 with 7 RBI in the postseason). Despite his less impressive numbers, Matsunaka received his fourth consecutive (and fifth overall)
Best Nine Award as an
outfielder, making him only the third player after Akinobu Mayumi and Ochiai to receive the award at three different positions (he had won three as a first baseman and one as a designated hitter).
2007 The season proved to be a disappointing one for Matsunaka. Despite the high expectations placed upon the new trio of Matsunaka, Kokubo (who had returned to the Hawks after a stint with the Giants via
free agency) and newly acquired
Hitoshi Tamura that would comprise the middle of the order, all three missed significant playing time due to
injuries. Matsunaka put up his worst numbers since 2002, hitting just .266 with 15 home runs and 68 RBI.
2008 Coming off of a rigorous off-season lower body
training regimen, Matsunaka rebounded in , hitting his 300th career home run against young Lions
ace Hideaki Wakui on August 29 and playing all 144 games while batting .290 with 25 home runs and driving in 92 runs. However, his personal accomplishments were offset by the Hawks' collapse in the second half of the season, a free-fall which culminated in a loss to the
Tohoku Rakuten Golden Eagles in the last game of the regular season that brought their first last-place finish since the 1996 season.
2009 Matsunaka was officially listed as an outfielder from the season onwards. He recorded his 1000th career RBI in the season opener against the
Orix Buffaloes on April 3 and became only the 11th player in NPB history to record 100 career
hit-batters on April 21 against the Fighters, hitting a pair of two-run homers in the same game. He got the 1500th hit of his career on May 6 against the Buffaloes, becoming the 100th player in NPB history to accomplish the feat. ==International career==