Without warning, the AL West has become a race once again: With Seattle’s four-game sweep of the division-leading Astros and Oakland taking two of three from the Angels, the Astros no longer have the stranglehold they once had on the division. As such, we enter Monday’s action with Houston leading the red-hot Athletics by just 2 ½ games in the West, with the Mariners only four games out of first. And for the A’s and Mariners, this week will be crucial to their postseason dreams.

Despite dropping four straight to Seattle, Houston remains on top of the West at 73–46, the second-best record in the majors (albeit distantly, with Boston destroying all comers at 85–35). Oakland’s 8–7 win over Los Angeles on Sunday was its 70th victory of the season, more wins than the A’s logged in either 2015 or ’16 and just five away from last year’s total. And Seattle has momentarily turned around a sluggish second half by sweeping the Astros and now sits at 69–50. Mariners fans will be thrilled to learn that record would put them in first place in literally any division but the AL East or West; here, it’s only good enough for third (and not even a playoff spot).

Despite the tightening of the West, the projection systems still see this as a walk for the Astros. FanGraphs’ odds give Houston a 93.6% chance to win the division, with the A’s at 4.3% and the Mariners barely alive at 2%. Baseball Prospectus gives Oakland more of a shot, tagging the Astros as the favorites with 86.6% odds, followed by the A’s at 10.6%. Seattle once again is the longest of long shots, checking in at 2.8%.

That’s on par with the season as a whole. Per FanGraphs, the Astros’ odds of winning the West have never dipped below 85.8%. That came all the way back on April 16, when Houston trailed the Angels (remember when they were contenders?) by three games. Los Angeles has long since faded, and despite some bumps on the way, the Astros settled into first place alone on June 14 and haven’t left that spot since.

Houston’s lead was as big as six games after July 24, but it’s shrunk due to a pair of losing streaks (five games in late July and four games now) and Oakland’s absurd second half. The A’s are 15–6 since the All-Star break, and since bottoming out both in record and the standings on June 15 at 34–36 and 11 ½ games out of first, Oakland has gone 36–12. In that time, the Athletics’ playoff odds have gone from a meager 3.1% to 59.3%, as they’ve seized control of the second wild card.

Seattle, meanwhile, has lost the plot. On July 1, the Mariners were sitting pretty at 54–31, just half a game behind Houston in the West and holding a commanding eight-game lead over Oakland for the second wild card. Things have gone sour since, as the Mariners are 16–19 over the last six weeks and an even .500 since the All-Star break. Once seemingly assured of ending a 16-year postseason drought, Seattle is now looking up at the A’s in the wild-card standings, trailing by 1 ½ games. Concurrently, the Mariners’ playoff odds have gone from a season-high of 88.3% on July 5 to a decidedly weaker 41.3 today. The A’s and M’s have been ships passing in the night the last six weeks—one headed for comfortable port, the other steering dangerously close to the rocks.

For Seattle, then, this weekend’s sweep of Houston was absolutely crucial. The Mariners’ playoff odds bottomed out to 26.1% last Thursday after an 11–7 loss to Texas—one that saw Felix Hernandez mercilessly shelled and subsequently booted from the rotation—dropped them eight games back of Houston in the West and three behind Oakland in the wild card. Thanks to some clutch hitting and relief work, though, the Mariners are still in the hunt—and this week offers them a chance to take control once more.

Indeed, this week’s action will be a crucible of sorts for both the A’s and Mariners, who meet in Oakland for a three-game set that will either narrow the wild-card standings even further or blow them apart. Things get even trickier for the Athletics after the Mariners leave town, as Houston will then visit for a three-game set that could very well finish off the division race.

For the A’s, it’s a week that could give them a golden chance to seize their own fate, or prove a fatal pitfall to their charmed season. But even beyond this week, there’s still plenty in the schedule to help and hurt each team. Both Houston and Seattle have 43 games left in its season; Oakland has 44 to go. Here’s how many are left versus above and below .500 teams, as well as head to head.

TEAM vs. >.500 vs. <.500 vs. HOU vs. OAK vs. SEA HOU 20 23 — 6 6 OAK 22 22 6 — 10 SEA 25 18 6 10 —

The final six weeks favor the Astros slightly in terms of quality of opponent left. The last week-plus of the season is particularly a gift: three against the Angels, three in Toronto, and four at woeful Baltimore. A three-game set with Boston is also on the docket, but the Astros’ road is easiest. It helps that they only have six head-to-head games apiece remaining against the teams chasing them in the standings, leaving both precious little ground to make up.

In comparison, Seattle faces a true gauntlet: Beginning with this week, the Mariners will play three at Oakland, three against the Dodgers, three against the Astros, and three at Arizona. They’ll also get three games against the Yankees in early September at home. Seattle will get some breaks in there: a pair of two-game series versus San Diego, three against Baltimore, and seven games against last-place Texas in the last 10 days of the season. But their path is the toughest.

Oakland lies in the middle, albeit with two rough stretches to navigate: this week at home against Seattle and Houston, and a run from Aug. 27 through Sept. 5 against the Astros, Mariners and Yankees—the latter two at home. What will be crucial for both the A’s and M’s will be the 10 games left against each other—plenty of chances for either to steal away the second wild card.

That’s the unfortunate reality for whichever two teams don’t finish first: they’ve only got one playoff spot left between them. The 74–43 Yankees are a virtual lock for the first wild card, and even if they somehow come back to win the AL East, the Red Sox would simply take their place.

That being the case, we may see some history. If current paces hold, Houston, Oakland and Seattle would finish with 99, 96 and 94 wins, respectively. Since realignment in 1994, only once has a division seen three teams win 94-plus: the 2015 NL Central, when the Cardinals (100) edged out the Pirates (98) and Cubs (97). Both Pittsburgh and Chicago, though, made the playoffs as the two wild-card teams, as the next highest non-first-place win total in the NL that year was San Francisco’s 84. This year’s AL West combatants will have no such luck.

So there you have it: The stakes for the West are sky-high both this week and going forward. Three teams enter, but only two will make it to October. As far as division and playoff races go, you can’t ask for much more.