The Seattle Mariners were the dominant heavyweight of 2003. The won 32 title bouts, twice as many as their nearest rival, the Oakland A's. All 32 victories came in the first half of the year.
The year was a bit unusual, in that there were two separate pivot games. The NL grabbed the crown on June 29, when the Padres beat the Mariners, 8-6. However, due to a makeup interleague game, the AL was able to grab the crown back on September 1, when the Red Sox beat the Phillies, 13-9.
That unusual fact helped create another unusual fact: the Devil Rays ended the regular season as champions. That sure sounds strange, doesn't it?
2003 Heavyweight of the Year: Seattle Mariners
Final 2003 Regular Season Champ: Tampa Bay Devil Rays