PITTSBURGH -- The performance of the Pirates’ rotation has left nothing to be desired over the first four weeks of the season. Their starting pitching has put together the best ERA in the National League, and their advantage over the NL’s next-best staff is a full run.

But Trevor Williams would’ve had to be nearly perfect to win on Tuesday night at PNC Park.

Williams recorded his fifth quality start in his fifth outing of the season, allowing two runs over seven strong innings, but the Pirates left seven runners on base and lost, 2-1, to the D-backs.

The Pirates’ rotation has put together a 2.26 ERA, yet Tuesday’s loss -- their third straight on the heels of a five-game winning streak -- dropped the club’s record to 12-9. The Pirates have scored three runs or fewer in 10 of their 21 games this season.

“It’s baseball. There’s going to be changes throughout the year. We’re going to be giving up some runs and the offense is going to pick us back up,” said Williams, who owns a 1.67 ERA in 18 starts dating back to July 11. “It’s the ebbs and flows of the season. We’re going out and giving it our all every day. It’s just baseball.

“It’s tough, but we’re playing some competitive baseball. We’re going to have some tough-luck losses, and we’re going to have some great wins as well by one or two runs.”

Sixteen of the Pirates’ first 21 games have been decided by one or two runs or in extra innings. They’ve consistently played games so close that one hit, one converted opportunity with a runner on second or third base, can swing the outcome.

Francisco Cervelli produced Pittsburgh’s only run of the night, ripping an RBI double to the notch in left-center field after Colin Moran reached on an infield single. But the Bucs finished 1-for-10 with runners in scoring position, and that one hit -- a Gregory Polanco single in the third inning -- didn’t drive in a run.

“Most of the games that we’ve played this year, they’ve been [within] one run. We’ve got to do a better job hitting,” Cervelli said. “I’ve got to do a better job hitting. I’ve got to execute. I’m not doing my job. Stay positive, come back and do it again.”

In the first inning, Pittsburgh stranded Melky Cabrera at second base after a one-out double that nearly cleared the Roberto Clemente Wall. In the second, Cervelli was left standing on second after Cole Tucker and Williams struck out. They put runners on the corners with one out in the third, but Josh Bell went down swinging and Moran grounded out into the D-backs’ well-positioned shift.

Immediately after that, the D-backs took advantage of a scoring opportunity. With a runner on second and two outs in the fourth, Arizona right fielder Adam Jones smacked a sinker below the zone into right field for a game-tying RBI double.

“We had an opportunity to score a run, then we didn’t and they did. Kind of flipped some momentum right there,” Pirates manager Clint Hurdle said. “The ability to score runners from third with less than two outs is always going to be critical in low-scoring games.”

D-backs starter Luke Weaver settled in after throwing 56 pitches in the first three innings, and the Pirates didn’t create another chance until the eighth. By that point, Arizona had pulled ahead. Jarrod Dyson worked a one-out walk in the sixth and moved to third on an Eduardo Escobar double, then Dyson sprinted home on a David Peralta grounder and slid to beat Cervelli’s tag at the plate.

Bell came to the plate with runners on first and second in the eighth, but reliever Archie Bradley struck him out with a high fastball. The Pirates provided one last glimmer of hope in the ninth, when Jason Martin walked and took second on a wild pitch.

But D-backs closer Greg Holland struck out Cervelli, and Hurdle sent up pinch-hitter Jung Ho Kang in place of switch-hitting shortstop Tucker. Kang flied out to right field to end the game.

“Holland’s been somewhat of a reverse-split guy, and Kang’s actually seen him,” Hurdle said. “Tried to give it a shot, maybe ride a longball out of there.”

Reynolds exits with injury

The Pirates are built to out-pitch opponents, not out-slug them, but supporting that pitching is an increasingly difficult task for a lineup beset by injuries. The Pirates saw right fielder Polanco and backup catcher Elias Diaz return on Monday, but now they may be without rookie center fielder Bryan Reynolds for at least a few days.

Reynolds pulled up holding his left leg after a single to right field in the fourth inning, and the Pirates took him out of the game as a precaution due to left quad discomfort. Pittsburgh is already playing without center fielder Starling Marte (abdominal wall contusion, bruised quad), left fielder Corey Dickerson (strained shoulder) and fourth outfielder Lonnie Chisenhall (fractured finger).