Five moments from MLB's first half that could end up deciding a pennant race

While August and September are when memories are made, they're not the only months that shape the postseason picture: There are 2,430 games on the Major League calendar, after all, and this year has already given us plenty of moments that will go a long way toward deciding who's in and who's out.
Here are five to remember before we hit the hothouse of pennant race season: 
April 2: D-backs 8, Dodgers 7 (15 innings)
The Dodgers entered 2018 as the prohibitive favorites in the NL West, the reigning NL champs who'd just come within one win of a World Series title. But they got an abrupt wake-up call in their first series of the season: The D-backs were for real, and they weren't going to concede anything.
L.A. took a 6-3 lead into the ninth, which -- with All-Star closer Kenley Jansen on the mound -- seemed decisive. But Arizona got the tying run to the plate, and then, with two outs, Chris Owings pulled off the unthinkable:

The game went all the way to the 15th, where again the Dodgers took a lead with a chance to close things out ... and again couldn't get the job done:

That finish would end up being emblematic of L.A.'s slow start: Jansen blew two saves and allowed six earned runs in April, and the same Dodger bullpen that was elite last year now finds itself 14th in ERA. And with L.A. holding a mere half-game lead over the D-backs entering play Friday, those blown leads could loom very large down the stretch.
June 6: Astros 7, Mariners 5
Both Houston and Seattle look like safe bets to make the postseason, but there's still the matter of which one will win its division -- and which one will have to survive a winner-take-all Wild Card Game. The two teams will play each other a whopping 13 times in the second half, but June 6 might end up as the most important day in the AL West race.
The Mariners had ample opportunity to come away with a win in Houston: They took a 4-3 lead into the eighth, and then -- after an Astros rally gave them a 7-5 lead -- brought Nelson Cruz to the plate as the winning run in the ninth. Alas, it wasn't to be:

But this wasn't just a missed opportunity for Seattle -- it also marked a turning point for Houston. Ken Giles' struggles left the Astros in search of stability in the closer's role, and on June 6, they finally found it: That was Héctor Rondón's first save of the year, and he's since gone on to record six more to go with a 1.62 ERA.
June 11: Cubs 7, Brewers 2 (11 innings)
Jason Heyward's career slash line against left-handed pitching: .232/.307/.346. Lefty hitters' career slash line against Brewers reliever and dark-horse NL Cy Young candidate Josh Hader: .105/.244/.114, with 60 K's in 128 plate appearances.
So, naturally, when Hader faced Heyward with one out in the eighth inning and the tying run on second, Heyward laced a single to right:

The game went to extras, where the Cubs eventually put up a five-spot to come away with a 7-2 win -- a win that looms pretty large right now, with Chicago just a game back of Milwaukee in the NL Central and plenty more crunch-time faceoffs with Hader still to come.
June 20: Yankees 7, Mariners 5
We're sorry, Mariners fans: Your team has been arguably the best story in baseball this year, and again, it's in great shape to make the postseason! But Seattle is currently four games back of the Yankees for the first AL Wild Card spot, and you can bet the club would love to have this game back.
After dropping game one of the series, Seattle was in control all night, taking a 5-3 lead heading into the bottom of the eighth ... at which point things promptly went off the rails. The Mariners' bullpen has been one of MLB's best this year, but Alex Colomé gave up a game-tying dinger to Gary Sánchez:

Then Ryan Cook surrendered the walk-off to Giancarlo Stanton an inning later:

Seattle lost the final game of the set the next day, but it does get New York at Safeco Field in early September -- and given how good the Yankees have been at home this year, that series could be huge.
July 1: Phillies 4, Nationals 3 (13 innings)
At the start of this four-game set on June 28, Washington sat two games back of the Phillies and four back of the Braves, having finally crawled out of its early-season hole. The Phillies, meanwhile, were struggling, having gone just 10-13 so far in June.
By the end of the series, though, things were far different. Philly took two of the first three, and the final game went all the way to the 13th thanks to some solid bullpen work. And then Andrew Knapp stepped up:

Two weeks later, that looks like an inflection point in the NL East race: Philly sits atop the division, while the Nationals are 5 1/2 games back.