For the Oakland Athletics and Seattle Mariners, the MLB season is already under way. Those two teams duked out a two-game series in Tokyo last week, with Seattle sweeping the season's first battle.

But for the other 28 MLB teams the start of their campaign is only a matter of days away. It's time for MLB excitement to truly begin.

The supercharged Boston Red Sox will be out to defend their World Series victory, but challenging them will be a host of hungry teams. There are certain to be gripping contests that come down to the wire this year.

Here we look at five compelling storylines you must watch for this season.

1. The National League Divisions Will Boast Tight Races

Last season the National League came down to the wire in both the Central and the West. The Chicago Cubs and Milwaukee Brewers and Los Angeles Dodgers and Colorado Rockies had to play in tense one-game playoffs for the division.

That could very well happen again this year, with the East also looking tighter for 2019. Bryce Harper completely changes the face of the Phillies, Atlanta will remain super competitive, and even the Mets look to be an improved club sporting a bolstered infield and bullpen.

There are some bad teams in the NL.  But there are a lot of sides that have seriously improved. The Central features threatening Cubs and Brewers teams, and the St. Louis Cardinals added an MVP candidate in the illustrious hitter Paul Goldschmidt. Plus, the Cincinnati Reds are no longer pushovers due to trades netting a variety of skill sets in Alex Wood, Yasiel Puig, Matt Kemp and Sonny Gray.

In the West, the Los Angeles Dodgers are the two-time defending NL champs seek to secure a three-peat. Meanwhile, the Rockies have one of the more underrated young rotations in all of baseball. And while the Arizona Diamondbacks lost their two best players in Goldschmidt and A.J. Pollock, they still have a solid top of the rotation and a competitive lineup with the potential to sizzle at times.

2. Here Come the Prospects

The current service-time rules continue to rob MLB of great young players early in the season. Cubs fans missed out on Kris Bryant early in 2015, and Braves loyalists did not get to see Ronald Acuña Jr. immediately last season. 

Nothing will change in 2019.

Vladimir Guerrero Jr. - with the potential to remind people seriously of his Hall of Fame father - and Eloy Jiménez have already been sent down to the minors by the Toronto Blue Jays and Chicago White Sox, respectively. And, the San Diego Padres are expected to do the same with Fernando Tatis Jr., another legacy player with huge potential on the field. 

Just how good will these players be when they inevitably get called up? Guerrero is coming off a year in which he batted .402 at Double-A as a 19-year old. Jimenez hit .355 at Triple-A and, though Tatis was not quite as impressive, an .862 OPS as a 19-year-old in a full Double-A  season reveals great potential.

Could be the best rookie class MLB has seen since 2015 when Carlos Correa and Francisco Lindor came up in the American League? That's without mentioning Forrest Whitley of the Houston Astros, Nick Senzel of the Reds and Victor Robles of the Nationals — with the latter likely to start on day one. 

3. One Crazy Trade Deadline

One of the changes MLB has already instituted this year is the removal of the waiver trade deadline at the end of August. Teams can now only make trades before July 31. The deadline has been seriously crazy over the last few years. How hectic will it be now that teams have just one chance to make moves?

        View this post on Instagram                   These teams made moves in the offseason. Who will take the next step toward October? A post shared by MLB ⚾ (@mlb) on Mar 23, 2019 at 9:44am PDT

4. The Rays and The A's Stepping It Up?

If you claim the Tampa Bay Rays and Athletics did not surprise you last year you are either a) a fan of those teams or b) a liar.

Both teams eclipsed 90 wins when neither was expected to win more than 80. The Rays' talented hurler Blake Snell won the AL Cy Young Award and Bob Melvin - not the world's flashiest manager - won Manager of the Year for the Athletics.

Snell has the potential to regress after his superb 2018, when he boasted a sparkling 1.89 ERA. But his 2.95 FIP projects a still impressive sub-3.00 ERA, especially in the hyper-competitive AL East.  

On the other hand, the Athletics' opening day starter Mike Fiers struggled in a loss to the Mariners in Tokyo. His position as their ace, especially in light of his 4.75 FIP last year, does not inspire confidence in the team's pitching depth.

Still, with trades having significantly affected the rosters of two teams who are each in tough divisions, it will be interesting to see if either can sustain their underdog success.

5. For These Teams It's Still Looking... Not So Good

MLB players cannot stop talking about the problem of non-competitive teams. And they are not wrong to draw attention to the amount of clubs likely to struggle in 2019.

We are coming off the first season since the schedule was extended to 162 games in which eight or more teams lost at least 95 games. Three finished with a pitiful 100 or more losses.

The Baltimore Orioles, Blue Jays, Kansas City Royals, White Sox, Texas Rangers, Detroit Tigers and San Francisco Giants are all in serious risk of losing 95 games again. It indeed may be even more surprising if the Royals and Orioles do not lose 100, considering the competition. 

Will these teams strive for improvement this season despite the incentive to keep losing and score higher draft picks?

We'll only know as the 2019 season begins to unfold starting this week.

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