With only four weeks left in the Major League season, every series featuring a postseason contender is obviously important -- but some carry a bit more weight than others.

Here's a look at six series this week that could have significant implications on various postseason races, though it's worth noting that there were a few others that narrowly missed the cut, including the Yankees-Mets showdown at Citi Field this weekend. The other matchups that received consideration are at least mentioned within the breakdowns of related series.

Rays-Red Sox (Monday-Wednesday)

Why it matters
The Rays have opened up a sizable lead in the AL East and the Red Sox have started to create some separation for the final AL Wild Card spot -- but each club still has work to do. Tampa Bay is eyeing not only the best record in the AL, but across the Majors as a whole -- something that would allow the Rays to secure home-field advantage throughout the entirety of the postseason. Boston, meanwhile, is still in a battle to move up to the first Wild Card spot, which would give the Red Sox home-field advantage in a potential AL Wild Card Game.

Other teams that will be watching closely

Athletics, Blue Jays, Mariners, Yankees
Though the Red Sox and Yankees have opened up a bit of a gap in the Wild Card hunt, the A's, Mariners and Blue Jays all remain very much in the race. The Yanks are also trying to hold off the Red Sox for that top AL Wild Card spot to ensure a potential AL Wild Card Game would take place in the comforts of Yankee Stadium. It's also worth mentioning that the Blue Jays will be hosting the Yankees for a three-game set from Tuesday-Thursday during the last week of the season in another series that will certainly have a significant impact on this Wild Card chase.

Players to watch
Rays shortstop Wander Franco continues his sensational rookie season, having reached base safely in 35 consecutive games entering this week -- but extending that streak won't come easy. Red Sox ace Chris Sale, who is 3-0 with a 2.53 ERA in four starts since making his return from Tommy John surgery, will take the mound for Monday's series opener.

Offensively for Boston, Rafael Devers has somewhat quietly put together another incredible season, racking up a career-high 33 homers to go along with 100 RBIs to this point. It's his second 30-homer, 100-RBI campaign, as he had 32 home runs and a career-best 115 RBIs in 2019.

How to watch
Monday's game between the Rays and Red Sox will be featured on ESPN, while the entire series can be seen live on MLB.TV.

Dodgers-Cardinals (Monday-Thursday)

Why it matters
The Cardinals have surged their way into the NL Wild Card race -- but this could be a make-or-break week for St. Louis. The Cards open with a tough four-game set against the Dodgers -- who are locked in a tight battle of their own atop the NL West -- before rounding out the week with a showdown against the fellow NL Wild Card hopeful Reds.

Other teams that will be watching closely

Giants, Padres, Phillies, Reds
The Giants entered the week with a one-game lead over the Dodgers in the NL West -- and in the race for MLB's best record. Meanwhile, the Cardinals have battled their way back into the thick of the Wild Card race. They sit three games back of the Padres for the final NL Wild Card spot, but they also need to leapfrog the Reds and Phillies.

Players to watch
Max Scherzer will continue his push for the NL Cy Young Award in Monday's series opener. He's been nearly untouchable since joining the Dodgers, going 4-0 with a 1.29 ERA in six starts. The three-time Cy Young Award winner has racked up 50 strikeouts over just 35 innings during that span.

The Cardinals will have a veteran ace of their own toeing the rubber on Wednesday, when Adam Wainwright gets the call. The 40-year-old right-hander has a 2.91 ERA this season, including a ridiculous 1.54 ERA over his last nine starts.

How to watch
The entire series can be seen live on MLB.TV, while Thursday's finale will also be televised on MLB Network.

Mariners-Astros (Monday-Wednesday)

Why it matters
Though the Astros have pulled away from the A's and Mariners a bit in the AL West, they are still locked in a tight battle with the White Sox for postseason positioning. Assuming neither the Astros nor the White Sox catch the Rays, they are on a path to play one another in the AL Division Series -- thus, the club with the better record would have home-field advantage in that potential matchup. As for the Mariners, they remain in the hunt for an AL Wild Card spot, but they have some work to do.

Other teams that will be watching closely

Athletics, Blue Jays, Red Sox, White Sox, Yankees
While Seattle and Houston battle it out, the A's and White Sox will be matching up in a three-game set of their own from Tuesday-Thursday -- a series that easily could have been featured here. Each series has nearly identical circumstances, with the Astros and White Sox battling for postseason positioning, while the Mariners and A's are scrapping to stay within striking distance of the Yankees and Red Sox in the AL Wild Card race.

Players to watch
Kyle Seager (33 homers) and Mitch Haniger (30) have both set career-high totals for home runs this season for the Mariners. Meanwhile, Astros shortstop Carlos Correa has two homers in his last three games and is hitting .297 with a .902 OPS over his last 24 contests.

How to watch
Monday's series opener will be on MLB Network and it will also be featured as the MLB.TV Free Game of the Day. Tuesday's game is also available on MLB.TV, while Wednesday's contest will air exclusively on YouTube.

Phillies-Brewers (Monday-Wednesday)

Why it matters
Every time the Phillies seem to fall out of the NL East race, they surge their way back into the picture. They are also still in the mix for the second NL Wild Card spot, but this could be a pivotal series before their schedule softens up again. Following this three-game set in Milwaukee, Philadelphia will play 20 of its final 23 games against teams currently outside of the playoff picture.

Other teams that will be watching closely

Braves, Cardinals, Dodgers, Giants, Mets, Padres, Reds
Though the Phillies' schedule eases up once they get through this series, they need to make sure they don't stumble too much against the Brewers -- or the Braves might make the Phils pay. Atlanta is entering a favorable stretch of its own, kicking off a 10-game homestand against the Nationals, Marlins and Rockies. The Cardinals, Mets, Padres and Reds will also have an interest in this one as they all remain in the mix -- along with the Phillies -- for the final NL Wild Card spot. As for the Dodgers and Giants, they are not only trying to hold off each other for the NL West crown, but they also need to keep the Brewers at bay in the race for the NL's best record.

Players to watch
The Phillies shuffled their rotation this weekend to line up Zack Wheeler to pitch in some of their biggest games down the stretch, starting with Monday's tilt against the Brewers. That shakeup results in an incredible pitching matchup for the series opener, as Milwaukee will counter with fellow NL Cy Young Award candidate Brandon Woodruff.

Of course, it's also worth keeping an eye on Bryce Harper. The Phillies outfielder is hitting .301 with a .998 OPS, and he's been particularly dominant since the All-Star break, hitting .331 with a 1.140 OPS over 47 games.

How to watch
The entire series can be seen live on MLB.TV.

Reds-Cardinals (Friday-Sunday)

Why it matters
The Reds and Cardinals are among the teams locked in a tight battle for the final NL Wild Card spot as the rivals meet for the final time this season.

Other teams that will be watching closely

Mets, Padres, Phillies
Pretty simple list here. With the first NL Wild Card all but certainly going to whichever team finishes as the NL West runner-up, that leaves five clubs -- the Reds, Padres, Cardinals, Phillies and -- battling for the final postseason spot. The Phillies and Mets are also still within striking distance of the Braves in the NL East, while the only path for the Reds, Padres and Cards is likely via the second NL Wild Card spot.

Players to watch
Paul Goldschmidt has been red-hot for the Cardinals, hitting .328 with seven homers, 27 RBIs and a .991 OPS in 31 games since the start of August. As for the Reds, Tyler Naquin had cooled off following his scorching start to the 2021 season -- but he's once again heating up, hitting .410 with a 1.241 OPS and six home runs over his last 23 games.

How to watch
The entire series can be seen live on MLB.TV.

Padres-Dodgers (Friday-Sunday)

Why it matters
It may not matter for the reasons many thought it would back in April, but this September showdown still carries massive postseason implications for both the Padres and the Dodgers. San Diego is fighting just to sneak into the playoffs as the second NL Wild Card team, while Los Angeles finds itself in a tight battle with San Francisco in the race for NL West supremacy -- and MLB's best overall record.

Other teams that will be watching closely

Cardinals, Giants, Mets, Phillies, Reds
The Giants have interest in what the Dodgers are doing for obvious reasons, while the other four clubs listed here will all be keeping an eye on the Padres as the NL Wild Card race continues down the stretch.

Players to watch
This series could very well feature the eventual NL MVP and NL Cy Young Award winners. Padres superstar Fernando Tatis Jr. remains the favorite for the NL MVP Award, while Dodgers righty Walker Buehler -- who is lined up to pitch Friday's opener -- is the frontrunner for the NL Cy Young Award. Fellow Cy Young candidate Max Scherzer is also likely to pitch one of the weekend games.

How to watch
The entire series can be seen live on MLB.TV, including Friday's opener being featured as the Free Game of the Day.