The World Series champion Chicago Cubs return their core but didn't rest on any laurels as they open a new season with a title to defend for the first time since 1909.Chicago not only has the ingredients for a second straight 100-plus victory season and National League Central title but enough to possibly make it back-to-back World Series appearances for the first time the opening decade of the 20th century.These 21st century Cubs start with the reigning NL Most Valuable Player (third baseman Kris Bryant), a World Series MVP (second baseman-outfielder Ben Zobrist) and not one but three Cy-Young caliber starting pitchers and four hurlers with 15 wins or more.Chicago also had one of baseball's best defensive groups with five Gold Glove finalists, a plus-282 run differential that was by far the best in the majors, and was tough to beat at home, going 57-24 at Wrigley Field for a franchise record for wins there.While the Cubs rate the early edge, manager Joe Maddon recognizes the road back will be full of challenges."It's hard, it's a gauntlet, you just don't win the National or the American (and) play seven games and go home," Maddon said earlier this spring. "There's so many things that can play a role -- injuries will play a role, hot and cold. The year before when we lost to the Mets, (Daniel) Murphy could not have been hotter and their pitching staff couldn't have been better."Chicago won the NL Central with a big league-best 103-58 record, took three of four from the San Francisco Giants in the NL Division Series and beat the Los Angeles Dodgers in six games for the NL championship.In the World Series, the Cubs rallied from a 3-1 World Series deficit with three consecutive victories, including a memorable 8-7 win in 10 innings in Game 7 over the host Cleveland Indians.By necessity, the Cubs had to replace an outfielder (Dexter Fowler) and closer (Aroldis Chapman), who signed free agent deals with the St. Louis Cardinals and New York Yankees, respectively.They brought in 31-year-old outfielder Jon Jay from the San Diego Padres and right-handed closer Wade Davis, also 31, in a trade that sent Jorge Soler to the Kansas City Royals. Any rookie breakthrough onto the 25-man Opening Day roster may be be a long shot, but infielder/outfielder Ian Happ appears closest.The Cubs open as the favorite to win another NL Central title, but Maddon warns that challengers abound."I think there's a lot of parity," Maddon said. "You look at our division, Cincinnati and Milwaukee had tough years last year. But I'm here to tell you, heads up on Milwaukee. Pittsburgh will be back, maybe St. Louis."