CHICAGO -- They still have some work to do, but the D-backs put themselves in a really good spot by beating the White Sox, 15-4, on Tuesday night at Guaranteed Rate Field.

The win, combined with the Cubs' late-inning loss to the Braves, put the D-backs ahead of Chicago by a game for the second NL Wild Card spot -- and it’s really a two-game lead since they hold the tiebreaker over the Cubs.

It was an impressive victory for a D-backs team that just 24 hours ago watched an eighth-inning lead slip away at Yankee Stadium. Arizona dropped two of three in that series and when the White Sox scored three runs in the first inning Tuesday, things could have gone sideways in a hurry.

• Games remaining (5): at CWS (2), vs. HOU (3)
• Standings update: The D-backs (83-74) hold the No. 2 Wild Card spot. They are one game ahead of the Cubs (82-75) and also own the tiebreaker. The D-backs lead the Marlins (81-75) by 1 1/2 games and they are 2 games ahead of the Reds (81-77). Cincinnati and Miami hold the tiebreaker over the D-backs. Arizona holds the tiebreaker over the Cubs.

“I am so proud of these guys for fighting through some tough circumstances, tough outcomes in New York, getting here,” D-backs manager Torey Lovullo said. “Falling behind 3-0 … it didn't impact us at all. We went out and played our game, did our thing our way and won a baseball game.”

Here are two key things to know about tonight’s game:

1. Christian Walker reached some milestones
Outfielder Corbin Carroll gets a lot of the attention and rightfully so, just like Zac Gallen does on the pitching side of things, but first baseman Christian Walker is a huge part of why the D-backs are in postseason contention this year.

Walker had a career night Tuesday, hitting a pair of homers -- a solo shot in the second and a two-run shot in the sixth and sandwiched between that he had a three-run triple that keyed a six-run fifth inning.

“Clearly Christian Walker had the big blows today,” Lovullo said. “It was an unbelievable day for him. Christian Walker was perfect offensively for us.”

The homers give Walker 33 on the season and his six RBIs raised his season total to 103, the first time he has eclipsed the 100-RBI mark in his career.

“It makes me proud to think about,” Walker said of achieving a 30-100 season. “It’s something that I've had my eye on for a long time and especially at this level it's just a standard for corner guys. It's impossible without my teammates getting on base and it's a credit to the guys in front of me and the guys behind me. The hitting coaches, you know, are in the fight with us everyday grinding and getting us the reps. So very proud, but obviously couldn't have done it without my teammates and the support staff.”

2. There’s a competition of sorts for the third spot in the rotation
Gallen and Merrill Kelly are certain to get starts should the D-backs make the postseason, but certainly in the first round, the D-backs could need a third starter. Who that would be is less clear, but this week could go a long way towards deciding that.

One of the candidates, Zach Davies, started Tuesday and allowed four runs over three innings.

Another possibility, Ryne Nelson, came on in relief and allowed just one hit over 4 2/3 innings bolstering his case.

“Without him today we don’t win this game, for sure,” Lovullo said of Nelson.

Brandon Pfaadt, who starts Wednesday afternoon’s game, is another candidate who will get the chance to make his case.

“You got to do your job to continue to get the baseball,” Lovullo said. “And we're just going to read and react and we got to make some tough decisions here. That's what we do. It's my job. We got to win baseball games.”