The Cincinnati Reds enter a weekend series against the Arizona Diamondbacks in Phoenix looking to gain more ground in the tightening National League wild-card race.

The Reds have gained five games on the New York Mets this month, moving to within half a game of the Mets for the third NL wild-card spot on their off day Thursday when Washington beat New York.

Cincinnati will send right-hander Zack Littell (9-8, 3.52 ERA) to the mound in the first game of the series Friday. The Diamondbacks will counter with right-hander Ryne Nelson (6-3, 3.58).

"To be honest, I'm not worried about anybody but our team," Reds catcher Jose Trevino said. "Take care of what we have to take care of first. ... That's how I go about it, and how a lot of us are going about it.

"We're in a tight race. Do whatever we can to win a game. And whether another team wins or another team loses, it doesn't matter."

The Reds have gained ground on every contender since Aug. 11 and are the only team in the majors that not been swept this season.

Littell, who has established a career high in victories, will make his fourth start for Cincy after being obtained from Tampa Bay at the trade deadline.

He is 1-0 with two quality starts and a 3.06 ERA with the Reds, beating the Chicago Cubs in his first start Aug. 5 before a pair of no-decisions against Pittsburgh and Milwaukee.

Littell gave up one run on four hits to the Brewers the last time out and was in line for the victory until a ninth-inning throwing error by shortstop Elly De La Cruz enabled the Brewers to tie the game in their 6-5, 11-inning win.

"We've got to be a little crisper on defense," Littell said afterward. "We've got to be better as a pitching staff going out there and attacking guys. It's really all around. If you want to play October baseball, it requires that type of level of play."

Littell will make his second start at Chase Field this season after a quality start -- six innings, three earned runs -- in a 5-1 loss with the Rays on April 22. He is 1-1 with a 5.02 ERA in nine appearances (three starts) against the Diamondbacks. Arizona's Pavin Smith homered against him earlier this year.

Nelson has worked to expand his repertoire to accompany a 95-mph fastball, his most effective pitch and one he uses about 62 percent of the time, according to FanGraphs.

He threw 38 four-seam fastballs, 24 sliders and 19 cut fastballs in his last outing, a no-decision Saturday at Colorado. Nelson gave up four runs in 6 1/3 innings and was in line for the victory until the Rockies rallied for a 10-7 win.

"Get people off his fastball," D-backs manager Torey Lovullo said of the adjustment. "It's 95-plus, it has a lot of hop on it. It's top of the zone. You have to really be a good hitter and stay on baseballs, and when he is changing speeds side to side like that, it is very, very impressive."

Nelson was roughed up in his only previous start against Cincinnati on June 7, when he gave up seven runs and walked four in three innings of a 13-1 loss.