The talent-packed Washington Nationals, hard-luck Cubs and Seattle's maturing Mariners are among the clubs tipped to contend as the clock starts ticking Sunday on the 2015 Major League Baseball season. A game clock will time breaks between innings and pitching changes, and players could also face fines for time-wasting in the batter's box as MLB tries to speed up games that last year averaged more than three hours for the first time in history. Games themselves may unfold a bit more briskly, but it's still a marathon and not a sprint to reach the World Series that starts in October and could trickle into a November finish. As the San Francisco Giants and Kansas City Royals showed last year in their unlikely runs to a thrilling seven-game World Series won by the Giants, almost anything can happen in the course of that lengthy season.