Opposite dugout: Lack of ace has kept D-backs mediocre and out of playoff hunt

Manager: Chip Hale (1st season)

Record: 50-53

Last 10 games: 7-3

Who to watch: 1B Paul Goldschmidt (.342/.458/.592 with 22 HR, 77 RBIs), CF A.J. Pollock (.305/.361/.465 with 11 HR, 45 RBIs), LF David Peralta (.281/.351/.493 with 9 HR, 48 RBIs), RHP Rubby De La Rosa (8-5, 4.59 ERA), RHP Brad Ziegler (18 saves, 1.18 ERA)

Season series vs. Nationals: 1-2

Pitching probables:

Aug. 3: RHP Zack Godley vs. RHP Doug Fister, 7:05 p.m., MASN
Aug. 4: LHP Patrick Corbin vs. RHP Max Scherzer, 7:05 p.m., MASN
Aug. 5: RHP Rubby De La Rosa vs. LHP Gio Gonzalez, 7:05 p.m., MASN2
Aug. 6: RHP Jeremy Hellickson vs. RHP Joe Ross, 4:05 p.m., MASN

Inside the Diamondbacks:

The Diamondbacks have hovered around the .500 mark all year, and in the National League West, that just isn't enough to compete for a playoff birth. And they've been around that mark not just in their overall record, but in their season splits as well. Arizona went 42-45 in the first half of the season and are 8-8 since the All-Star break, including starting the second half of the season by getting swept at home by the Giants and later pulling off a six-game win streak. In 13 extra-inning games, the D-backs are 7-6, and they are 16-15 in one-run games and 13-12 in blowout games (five-plus run difference). They are even 26-27 at home and 24-26 on the road. So mediocrity has been this team's staple for 2015.

The mediocrity doesn't come from its offense, however. The Diamondbacks rank in the National League Top 5 in batting average, on-base percentage and slugging percentage (.261/.323/.402), and are second in the league in runs scored (451) and runs batted in (426). The Snakes are led by NL MVP candidate first baseman Paul Goldschmidt, who leads the league in batting average (.342) and who is second in RBIs (77) and fifth in home runs (22). He also has a a league-leading .458 on-base percentage and is second with a .592 slugging percentage to complete his batting line. Center fielder A.J. Pollock has been a major contributor as well, slashing .305/.361/.465 with 11 homers and 45 RBIs, but has been day-to-day with a hamstring injury. Although Pollock was out of the lineup for each of the past two days, he is expected to make an appearance some time during this series in Washington.

Goldschmidt and Pollock have made up most of Arizona's power since outfielder Mark Trumbo was traded to the Mariners in early June. Although, left fielder David Peralta has added nine homers and 48 RBIs while batting for a .281/.351/.493 slash line. On the right side of the outfield, Ender Inciarte is hitting well for a .290 average while driving in 27 runs. Third baseman Yasmany Tomas is batting .295 with 39 RBIs, while second baseman Chris Owings and shortstop Nick Ahmed haven't hit well for average (.230 and .221 respectively), but have combined for 50 RBIs.

Rookie right-hander Zack Godley will make just his third career start to open the series at Nationals Park. Drafted by the Cubs in 2013, Godley was traded to Arizona along with another minor league player for Miguel Montero. He is 2-0 with a 2.25 ERA to start his big league career after an impressive debut against the Brewers. On July 23, Godley pitched six innings, giving up only four hits, hitting one batter and striking out seven against Milwaukee for his first win. He followed that up by going another six innings, allowing seven hits (two home runs), three runs, three walks and four strikeouts in Seattle for his second victory. Right-handed batters are hitting .292 while lefties are only hitting .211 over his first two outings. The 25-year-old from the University of Tennessee throws a 92 mph fastball 43 percent of the time, a 91 mph cut fastball 35 percent of the time, and also mixes in an 83 mph changeup and 80 mph curveball.

Lefty Patrick Corbin will go head-to-head with Max Scherzer in Game 2 of this four-game series. Cobin made his return to the Diamondbacks rotation on July 4 after missing all of last year recovering from Tommy John surgery. Over five starts this season, he is 2-3 with an ERA of 3.21, sandwiching his three losses between his two wins. Although he did suffer that three-game losing streak, he only allowed four, two and one runs in those games, getting very little run support in low-scoring affairs. He doesn't fair as well away from Chase Field as he does in it, with a 4.09 ERA on the road versus 2.65 at home. Corbin hasn't faced the Nats since 2013, but is 1-1 with an ERA of 4.26 in three career starts against Washington, having given up home runs to Ian Desmond and Jayson Werth.

Rubby De La Rosa brings his team-best 8-5 record along with a 4.59 ERA in his first season with Arizona to face Gio Gonzalez in the third game. After losing his first two starts in July, De La Rosa has won two of his first three since the All-Star break with an ERA of 2.14. Nationals' left-handed batters probably can't wait to face De La Rosa, who is 2-4 with a 5.14 ERA on the road, at Nats Park. Lefties are batting .311 against the right-hander, while he's held righties to an average of just .213. De La Rosa pitched against the Nationals for the first time back on May 12. He went seven innings and gave up eight hits (including a home run to Bryce Harper), four runs, two walks and four strikeouts while taking the 14-6 win.

Jeremy Hellickson still hasn't lived up to the expectations in his first season with the D-backs since coming to Arizona via a trade with the Rays last offseason. Hellickson is only 7-7 with a 4.95 ERA, and will take on rookie Joe Ross to finish out the series in D.C. Hellickson is 1-2 over three starts with a 4.41 ERA since the All-Star break, which includes a 3 1/3-inning outing in Houston in which he gave up seven runs (six earned) on seven hits (three home runs). He may not be looking at a good chance to get any better at Nats Park as he is only 2-4 with a 5.94 ERA on the road. Hellickson too made his first start against Washington earlier this season. He pitched 5 2/3 innings while giving up four runs on four hits (including a Jayson Werth homer) with four walks, three strikeouts and a hit batter while getting a no-decision in the 9-6 loss.

Pitching has anchored Arizona down as a mediocre team. They only have a 4.07 team ERA while giving up the fourth-most earned runs in the National League. They are also allowing opponents to hit .258 against them, which is fifth-highest in the league. The Diamondbacks aren't getting enough out of their starters, who have only posted 45 quality starts this season, ranking 25th in the majors. The lack of a true ace in the rotation has kept the Snakes well out of competition for a postseason berth. While nine games back from the Dodgers in the West and 6 1/2 games away from the final wild card spot, if the pitching doesn't improve over these last two months, the Diamondbacks might need to look for that ace during this offseason.