PHOENIX — A few days ago, before the Phillies embarked on this West Coast trip, manager Gabe Kapler cited one of his favorite statistics — fielding independent pitching — to illustrate how well the starting rotation has been performing.

But with pitching as dominant as this, advanced metrics aren't required.

Nick Pivetta became the latest Phillies starter to turn out the lights on an opponent. He blanked the Diamondbacks for six innings here Tuesday night, outpitching Arizona ace Zack Greinke in a 5-2 victory that stretched the Phillies' lead in the National League East back to 1 1/2 games.

Over the last eight games, or nearly two full turns through the rotation, Phillies starters — Aaron Nola, Jake Arrieta, Pivetta, Vince Velasquez and Zach Eflin — have combined to allow nine earned runs in 55 1/3 innings for a 1.46 ERA. Next up: Velasquez, who will seek to give the Phillies another series victory Wednesday in the matinee finale at Chase Field.

"It's been awesome, especially for the defense out there. I'm able to just look at the birds," right fielder Nick Williams said, breaking into a laugh. "No, it's been great. It makes it easier on us. These pitchers, they're giving us energy because you know as hitters you want to back them up and put up runs."

For a second game in a row, though, the Phillies left their starting pitcher without margin for error. And for a second game in a row, their starter didn't need any.

Like Arrieta on Monday night, Pivetta was superb. His fastball crackled, averaging 95 mph and scraping 97, and he rode it for most of his six innings. He put runners on base in all but the fifth but escaped each time, including ground-ball double plays in both the second and fourth innings.

Pivetta had thrown 96 pitches when he got lifted for a pinch-hitter in the top of the seventh. At that point, the Phillies led 1-0 on Williams' third-inning home run against Greinke. It wasn't until after Luis Garcia tossed a scoreless inning that the offense poured it on, scoring four times in the top of the eighth against former Phillies reliever Jake Diekman.

"Greinke's an amazing pitcher, a top-tier starting pitcher, so you really have to be perfect when you're facing a guy like that," Pivetta said. "But the guys chipped away. Nick Williams got us ahead really early, and that was awesome. Just having that one-run lead really boosted my confidence and the team's confidence. All I had to do was just keep throwing up zeroes knowing we had that lead."

The rotation has led the way for the Phillies all season. As Kapler proudly noted, each of the five starters has a FIP of less than 4.00. Only two other teams — the Houston Astros and Cleveland Indians — can say the same of their rotations.

But this eight-game roll has been something to behold. It began July 30 at Fenway Park with Nola's eight-inning gem and continued right on through a four-game sweep of the Miami Marlins at Citizens Bank Park and the first two games of this series against the Diamondbacks.

Pivetta struggled through the middle part of the season. After posting a 3.26 ERA in his first 11 starts, he notched a 6.84 mark over his next 10 starts. But Kapler remained a staunch Pivetta supporter. After Pivetta gave up five runs in a loss in Cincinnati on July 27, Kapler used another advanced metric — expected fielding independent pitching (xFIP), which considers only the factors that a pitcher can control (home runs, walks, hit by pitches, strikeouts)  — to build an argument that Pivetta had pitched better than his traditional numbers indicated.

Entering Tuesday night, Pivetta had a 4.57 ERA but a 3.20 xFIP, which tied him with Indians ace Corey Kluber for 11th in the majors and put him percentage points ahead of Greinke (3.21) and Astros star Justin Verlander (3.22).

"The organization has continued to show a great degree of confidence in Nick Pivetta, and this is Nick kind of rewarding the organization for its patience," Kapler said. "He's been looking for ways to bring out these type of performances, studying really hard between starts, looking for ways to make adjustments, preparing his body physically. And it all showed up today for him."

Said Pivetta: "I haven't given in. I've just stuck with the process we have here. The team has really stuck with me. They've really helped me mentally get through what I was going through, and I think that's the biggest thing. I owe a lot to these guys in this room, and I think that's helped me out the most."

The seventh-inning outburst began with sloppy defense by the D'backs. Diekman made a low toss to first base on Cesar Hernandez's bunt, and after the ball skidded into right fielder, Steven Souza Jr. airmailed a throw to third base, allowing Hernandez to score.

Unlike Monday night, when the Phillies were unable to add on to a 2-0 lead for Arrieta, they continued their rally against Diekman. They loaded the bases for Asdrubal Cabrera, who drove in two runs with a double. Two batters later, Jorge Alfaro followed with an RBI single to make it 5-0.

The Diamondbacks broke through in the bottom of the eighth thanks to slipshod defense by the Phillies. Herrera was unable to haul in Paul Goldschmidt's drive to the center-field warning track, and third baseman Maikel Franco couldn't handle a bouncer.

But Pat Neshek closed out the game in the bottom of the ninth to give the Phillies their sixth win in seven games, a streak that has been built on the backs of the starting pitching.

"It's really nice when you have everybody kind of clicking together and doing really great things," Pivetta said. "We kind of feed off each other. It just helps each and every single one of us learn from what the other guys are doing well and make it happen in your next start."