Following Robbie Ray's lead, the Arizona Diamondbacks' rotation is finally rounding into form.

Seeking a fourth straight strong start, Ray attempts to pitch the Diamondbacks to a seventh win in eight games in Sunday's series finale with the Pittsburgh Pirates.

Of a group that added a former Cy Young Award winner in Zack Greinke and a 2015 All-Star in Shelby Miller, Ray (1-0, 1.96 ERA) has been the most consistent performer through the season's early stages. The 24-year-old has allowed two runs or less while working at least six innings in each of his first three starts, building off a solid 2015 finish in which he posted a 2.70 ERA over his final seven outings.

After no-decisions in his initial two starts, Ray cracked the win column in Tuesday's 3-0 victory at San Francisco. The left-hander yielded five hits and matched a career high with eight strikeouts in six innings.

''My breaking ball was the best it's been all year but mainly I was my fastball command,'' he said. ''Everything was working.''

Ray's gem began a five-game stretch in which Arizona starters have produced a 2.70 ERA after recording a 5.81 mark through the first 14. Rubby De La Rosa continued the trend in Saturday's 7-1 win, limiting the Pirates to a run on three hits and fanning six in six innings.

De La Rosa entered the game with an 8.44 ERA, while Pittsburgh (9-9) came in leading the majors in batting average and on-base percentage. The Pirates collected 15 hits and homered three times in winning Friday's opener 8-7.

Ray may get to face a Pirates lineup without its hottest hitter. John Jaso is batting .413 over a career-high 12-game hitting streak, but the first baseman normally sits against lefties.

Francisco Liriano continues to wield a dangerous bat, though. Sunday's starter is 4 for 6 with three RBIs at the plate this season and hitting .361 with a home run and 10 RBIs over his past 16 starts.

Liriano (1-1, 4.11 ERA) hasn't been as effective on the mound, issuing 14 walks and permitting three homers in 15 1/3 innings and missing a start with a sore hamstring. He walked five and allowed a pair of two-run homers in 4 1/3 innings during Tuesday's 5-4 loss at San Diego, his first appearance in 11 days.

Liriano has pitched well at Chase Field, where he owns a 1.96 ERA in three starts and held Arizona to two hits over 6 1/3 innings of an 8-0 victory on April 26.

David Peralta has homered in the series' first two games and Yasmany Tomas is batting .342 with three home runs over a nine-game hitting streak for Arizona (10-9). Neither has fared well against Liriano, with Peralta 0 for 5 with four strikeouts and Tomas 0 for 6.

Welington Castillo, who homered twice on Friday and has five in six games, is 4 for 15 versus Liriano.

Pittsburgh's Sean Rodriguez homered in a second straight game Saturday and has three and seven RBIs in his last 12 at-bats. He went 2 for 2 off Ray in a 4-1 victory Aug. 19.

"We're all happy for him, the way he's swung the bat," manager Clint Hurdle told MLB's official website. "It's been fun to watch."

The Pirates swept a three-game set at Chase Field last April and are 10-4 in their last 14 there.

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