The National League Wild Card matchup features two teams from the NL West, and the winner will move on to take on yet another NL West foe in the Los Angeles Dodgers in the NLDS.
The Arizona Diamondbacks pulled away from the rest of the field with a record of 93-69, reversing their record from a year ago when they went 69-93. They'll play host to the Colorado Rockies, who held off a couple of NL Central teams to advance into the postseason with a record of 87-75.
It's worth noting that these squads went in different directions following the All-Star break -- the DBacks went 40-33, while the Rockies put together a 35-36 record. But, as we all know, anything can happen in a one-game win-or-go-home scenario.
Why the Diamondbacks Will Win
Arizona will throw their high-priced ace Zack Greinke at the Rockies, who bounced back after a disappointing 2016 to go 17-7 with a 3.20 ERA and 215 strikeouts in 202.1 innings, resulting in an fWAR of 5.1. He not only enjoyed pitching at home -- where he posted a 13-1 record and a 2.87 ERA -- but he also liked facing Colorado this season. In five games that spanned 34.1 innings of work, the right-hander posted a 3.41 ERA with 37 strikeouts and just 2 walks, while Rockies hitters managed a meager .229/.241/.435 triple slash with an OPS+ of 69 against him.
Greinke has also proven to be a good postseason pitcher, evidenced by a 3-3 record and a 3.59 ERA in nine career starts.
Arizona features one of the game's great lineups, with perennial MVP candidate Paul Goldschmidt leading the charge. He hit .297/.404/.563 with 36 homers, 120 RBI, 18 stolen bases, a weighted runs created (wRC+) of 142 and an fWAR of 5.3. He was joined by perhaps the best midseason trade acquisition in recent memory, J.D. Martinez, who hit .303/.376/.690 with 45 homers, 104 RBI, and a wRC+ of 166 in just 119 games played. While he's only been with Arizona for 62 games, he still slugged 29 dingers and put up an insane .741 slugging percentage. A.J. Pollock, Jake Lamb and David Peralta fill out a DBacks lineup that scored the fourth-most runs in the National League this year.
Arizona's bullpen, while not elite, was effective for most of the season, with the second-best ERA in the NL (3.78). Fernando Rodney somehow saved 39 games with an ERA of 4.23, but Archie Bradley is really their only other top-notch reliever, with a 1.73 ERA this season. If they want to get deep into October, though, they'll need significant contributions from somewhere else in their bullpen.
Why the Rockies Will Win
Colorado's ace Jon Gray ain't no slouch.
He was limited to just 20 starts this season after landing on the disabled list with a stress fracture in his foot, but he ended up posting a 10-4 record with a 3.64 ERA and 112 strikeouts in 110.1 innings. Those are excellent numbers for a starter who is forced to call Coors Field home. He allowed more than three runs in just three of his 20 starts, and didn't do so once after the calendar flipped to July.
Gray also experienced some success against Arizona in 2017, going 2-1 with a 3.50 ERA against them, while opposing hitters mustered a .264/.308/.458 line.
Like Arizona, the Rockies feature a loaded lineup -- they led the NL in runs scored, with MVP candidates Charlie Blackmon and Nolan Arenado at the head of the class. Blackmon hit .331/.399/.601 with 37 homers and 104 RBI, but it is worth noting that he was much better at home (.391/.466/.773 slash line) than on the road (.276/.337/.447).
Arenado hit .309/.373/.586 with 37 bombs, 130 RBI, and 100 runs scored, and unlike Blackmon, his numbers at home (.336/.392/.644) weren't as drastically different to when he hit the road (.283/.355/.531). Trevor Story, DJ LeMahieu and Carlos Gonzalez round out a potent Colorado lineup.
While Arizona finished with the better bullpen ERA, the Rockies appear to have a more dynamic set of relievers that can be used in important situations. Greg Holland saved 41 games and posted an ERA of 3.61 this year, with Jake McGee, Pat Neshek, and Chris Rusin also providing some solid late-inning options for Colorado.
Who Will Win
The Diamondbacks finished the 2017 season with the better record and are the favorites on paper, with our metrics giving them a 59.74% probability of winning tonight's matchup.
Colorado is a much different team on the road, and the fact both squads went in different directions in the second half indicates the DBacks have more momentum heading into this game. However, one of Arizona's big advantages -- their starting rotation -- doesn't come into play in a one-game playoff, so this contest could potentially be determined by which starting pitcher is more effective in the earlier innings.