By Manny Randhawa

DENVER -- There are supposedly several factors working against the Colorado Rockies. Most prominently, there's Coors Field, where offense has a tendency to flare out of pitchers' control thanks to the thin mountain air and cavernous outfield. There's the lack of recent postseason success, with the club looking for its first playoff berth since 2009.

But none of that seems to matter to the 2017 Rockies, who are perched atop the NL West with the second-best record in the Majors (46-26) following one of the most exciting games in franchise history on Sunday.

Trailing the Giants, 5-4, in the ninth inning, Nolan Arenado hit a walk-off, three-run homer off closer Mark Melancon. The blast landed just over the left field wall to sweep San Francisco and vault Colorado to 20 games over .500 for the first time in this decade. To top it off, the homer gave Arenado the first cycle of his career.

One swing of Arenado's bat captured the very essence of the Rockies' season through 72 games, and may have awoken the wider baseball world to a notion that is becoming harder to ignore as we near the midway point of the season.

"We're for real," said Arenado after the game. "It's fun in Denver right now. I don't know how else to put it."

Arenado stood in front of his locker, still in full uniform after a curtain call on the field before 48,341 frenzied fans. He could hardly contain his glee despite his blood-stained jersey, the result of a cut above his left eye from the bill of center fielder Charlie Blackmon's helmet hitting Arenado during the wild celebration.

"That was one of the best moments in my career," Arenado said. "I've hit some big homers, but this was by far the best."

The man at the helm for the NL West frontrunners, manager Bud Black, makes it a point to downplay the effect of all those supposed stumbling blocks that ought to be hindering the Rockies' bid to finally win the first World Series championship in franchise history. Any time they're brought up, he steers the conversation back to a simple mantra: if you play well, you win most of the time, no matter what ballpark you're in.

So far, Black's doctrine is working. Rockies pitchers have the second-best ERA- (ballpark- and league-adjusted earned run average) in MLB, per Fangraphs (80).

"It's not the ballpark. It's the pitches," Black said. "These games [referring to the Rockies' 10-9 win over the Giants last Thursday after leading 9-1 at one point] happen at other places also, not just here."

There's always a certain amount of luck involved in reaching the postseason, and then winning there. Right now, everything is going Colorado's way. The Rockies were actually leading Sunday's game, 3-2, entering the ninth inning. But reliever Jake McGee, on because closer Greg Holland had thrown 58 pitches over the previous three games, relinquished that advantage. Despite the setback -- the second failure to hold a lead in four days -- Colorado roared back again.

Luck was a significant element of the comeback. According to Statcast™, Melancon yielded three straight hits -- soft singles by Charlie Blackmon and DJ LeMahieu, and the Arenado homer -- with hit probabilities of less than 15 percent. Blackmon's looper to center had a seven percent hit probability. LeMahieu's seeing-eye single to right has been a hit just nine percent of the time since Statcast™ was introduced in 2015.

Arenado's homer had an exit velocity of 93.2 mph (the softest Arenado homer Statcast™ has ever tracked) and a launch angle of 33 degrees. Batted balls with that exit velocity and launch angle since Statcast™ was introduced have gone over the wall just seven percent of the time.

But so it goes for the Rockies these days. There's actually reason to believe they could be even better in the second half of the season. This is a club with two of its starting pitchers rehabbing from injuries: Jon Gray and Tyler Anderson. Gray hasn't pitched for the Rockies since April 13 at AT&T Park, when he suffered a stress fracture in his left foot. Anderson has been sidelined with knee inflammation. Both could return within a week.

Sunday's starter, Tyler Chatwood, entered June as the proverbial Jekyll-and-Hyde of starting pitchers. He had surrendered four or more runs in seven of his 11 starts, and two or fewer in the other four. Since then, he has a 1.73 ERA in four starts.

And the traditional Rockies strength, a powerful offense, hasn't clicked on all cylinders yet in 2017. Carlos Gonzalez is slashing .219/.301/.335 with five home runs. He's currently mired in a 3-for-34 slump (all three hits being singles). Trevor Story, who electrified baseball by hitting 10 homers in his first month in the Majors last April, and 27 overall last season, is hitting .227/.318/.433 with 10 homers so far in 2017.

A strong core of rookie hurlers, including German Marquez, Antonio Senzatela, Kyle Freeland and Jeff Hoffman, have carried the rotation. And the bullpen, with a rejuvenated Holland at the back end, has been one of the best in baseball.

As the euphoria of Sunday's win gives way to a new week, the Rockies will look ahead to a showdown with another surprising NL West contender, the Diamondbacks, who come to Denver for a three-game set at Coors Field beginning on Tuesday.

The season is not yet halfway complete. But come October, should the Rockies find themselves in the postseason for the first time in seven years, we'll likely be looking back at Sunday's dramatic finish at Coors Field as the moment Colorado made believers out of us.

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Manny Randhawa is a reporter for MLB.com and a contributor to Sports on Earth. You can follow him on Twitter @MannyOnMLB.