The closer we get to October, the more critical each series becomes for teams in postseason contention. This week features several series with major playoff implications as we head into the final weeks of the regular season.

From the top two clubs in the American League East facing off to multiple series involving Wild Card hopefuls in both leagues, you don't want to miss what could very well be some of the most important and dramatic baseball of the entire season.

Here are five series to keep your eye on this week:

Braves at Phillies
4 games (Monday-Wednesday)

Head-to-head: The Braves have taken four of the six meetings between the two National League East rivals so far this season. Following this four-game set in Philadelphia, the clubs will meet for one more series during the regular season, from Sept. 18-20 in Atlanta.

Storyline: The Phillies were under .500 until mid-June, when the defending NL champions turned things around and vaulted themselves back into postseason contention. That's where they've stayed since then, and Philadelphia currently occupies the top NL Wild Card spot. The Phils finished strong in August, ending the month with wins in seven of their final nine games. They've stumbled a bit so far in September, dropping series to the Brewers and, over the weekend, the Marlins.

The Braves, meanwhile, continue to roll toward a sixth consecutive NL East title. With the best lineup in baseball and one of the best pitching staffs from top to bottom, there just doesn't seem to be a weakness on Atlanta's roster. With a victory over the Pirates on Sunday, the Braves became the first team to clinch a postseason berth this season.

Watch out for: Who else but Ronald Acuña Jr.? Heading into the final three weeks of the regular season, Acuña and the Dodgers' Mookie Betts are neck-and-neck in the NL MVP race. Beyond that, Acuña is continuing to make history with every home run he hits and every base he steals. Could he break the seal on the 40-homer/70-steal club? He's already inaugurated the 30/60 club, and he's only five homers and six steals shy.

Rangers at Blue Jays
4 games (Monday-Thursday)

Head-to-head: The Rangers won two of the three games these clubs have played against one another so far this season, winning a series at Globe Life Field from June 16-18.

Storyline: The Jays are hot. The Rangers are not. With a sweep of the Royals over the weekend, Toronto has won eight of its last 10 games. And while Texas won two of three against the A's over the weekend, the Rangers have been scuffling since mid-August -- since Aug. 16, they're 6-16.

With Bo Bichette back on the field after he was sidelined with a quad injury, the Blue Jays have overtaken the Mariners in the AL Wild Card standings. The Rangers, who occupied first place in the AL West for most of the season, find themselves three games behind the Astros in the division and a half-game behind the Mariners for the third Wild Card position.

Watch out for: One Ranger who hasn't struggled this month is Marcus Semien. The slugging second baseman has been red-hot in September, adding four hits -- including two home runs -- in Sunday's 9-4 win in Oakland. He's 14-for-38 with an OPS of 1.192 this month. With Adolis García and Josh Jung sidelined by injury, Semien's contributions have been crucial. Texas will need that to continue if it hopes to reach the postseason.

Marlins at Brewers
4 games (Monday-Thursday)

Head-to-head: This will be the first series between these clubs in 2023. They'll also play three in Miami from Sept. 22-24.

Storyline: The Marlins are playing well when it counts -- so far in September, Miami is 7-2, winning series against the Nationals, Dodgers and Phillies. The Brewers are coming off a heart-breaking loss in the Bronx, where they took a combined no-hitter into the 11th inning against the Yankees, only to see that broken up before losing to New York in 13 innings. Milwaukee is trying to hold off the Cubs, who continue to keep things tight in the NL Central, just three games behind the Brewers.

Watch out for: The Brewers' offense. Milwaukee has in recent years relied heavily on its strong pitching staff from top to bottom, and just enough hitting. But so far in September, the club's lineup has produced seven or more runs in five of nine games. And since Aug. 3, the Brewers rank 10th in MLB in runs scored. If that continues behind the pitching of Corbin Burnes (eight no-hit innings vs. the Yankees on Sunday), Freddy Peralta (2.09 ERA over his last eight starts) and Brandon Woodruff (2.78 ERA in six starts since coming off the injured list), in particular, the Brewers could be very dangerous in September and beyond.

Rays at Orioles
4 games (Thursday-Sunday)

Head-to-head: The Orioles have won six of the nine meetings between these clubs so far this season. This is the final regular season series between them.

Storyline: The AL East title could very well be decided by the outcome of this head-to-head matchup. The Orioles enter the week leading the Rays by three games in the division, and when the upcoming four-game set between them is complete, there will only be two weeks remaining in the regular season.

Watch out for: Left-hander John Means is slated to make his season debut for the Orioles on Tuesday at Camden Yards against the Cardinals. It'll be his first appearance for Baltimore since undergoing Tommy John surgery in April 2022, and if he proves effective, especially against the Rays this weekend, it could be a huge boost for a Baltimore club that has surpassed expectations with an unheralded starting rotation. Means was one of the Orioles' best starters from 2019-22, a period over which he posted a 3.72 ERA (124 ERA+).

Cubs at D-backs
3 games (Friday-Sunday)

Head-to-head: The D-backs took three out of four from the Cubs at Wrigley Field this past weekend, and they'll meet again for another weekend series with NL Wild Card implications abounding. Entering the week, Chicago is in possession of the second NL Wild Card spot, two games up on the D-backs, who occupy the third Wild Card position.

Storyline: Both of these teams have raised eyebrows around the baseball world this season -- the D-backs did that early on, entering the second half leading the NL West, and the Cubs have been surging since mid-July. While the Dodgers are closing in on another division title with a big lead over Arizona in the NL West, Chicago is just three games behind Milwaukee in the NL Central.

Watch out for: If you had to name one player who has been most crucial to the Cubs' success this season, it would be Cody Bellinger. The former NL Rookie of the Year and MVP fell on hard times from 2020-22, but he's bounced back in a big way with his new club in '23. Bellinger smashed his 25th home run of the season in Sunday's win over the D-backs at Wrigley Field, and he owns a 1.043 OPS with five homers already this month.