PHOENIX -- Most of Rockies right-hander Antonio Senzatela’s starts have ranged from competitive to outstanding. But some, like Friday night’s 8-0 loss to the D-backs at Chase Field -- the Rockies’ fourth straight defeat -- can be stunningly bad. Senzatela (7-6) saw a promising beginning unravel with Christian Walker’s two-run

PHOENIX -- Most of Rockies right-hander Antonio Senzatela ’s starts have ranged from competitive to outstanding. But some, like Friday night’s 8-0 loss to the D-backs at Chase Field -- the Rockies’ fourth straight defeat -- can be stunningly bad.

Senzatela (7-6) saw a promising beginning unravel with Christian Walker’s two-run shot -- the first of his two homers -- in the fourth inning, followed by a five-run fifth. The seven runs on seven hits in 4 1/3 innings marked the fourth time this season Senzatela has given up seven or more runs while lasting fewer than five innings.

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“I need to make a quality pitch every time, I need to get out of jams, I need to throw good every time,” Senzatela said. “Sometimes, these things happen.

“I’ve got to get it in my mind, if there’s a big inning, it’s just not big like this.”

The Rockies were looking for more from Senzatela, especially after a difficult 2-4 homestand during which the starters posted a 5.74 ERA.

Much of the Rockies’ hopes rest with Senzatela. Opening Day starter, left-hander Kyle Freeland, has spent much of the first half at Triple-A Albuquerque, although he looks to return after the All-Star break. Lefty Tyler Anderson is unlikely to return this season after undergoing left knee surgery. Righty Chad Bettis has transitioned to the bullpen. Righties Jon Gray and German Marquez -- who will start against the D-backs in the final two games before the break -- have been consistently solid. But the Rockies need more if they’re going to grab their third straight postseason berth.

When and where the bad outings occur is mysterious. Sure, Coors Field as a home park presents its difficulties, but he’s had two stinkers there, while two have been on the road.

Why they happen is no mystery.

“It’s just elevation of the fastball,” said Rockies manager Bud Black, whose team saw the end of club-record win streaks of eight games against the D-backs and six games at Chase Field. “He’s a guy who pitches very aggressively with the fastball. The slider and his secondary pitches are in the mix."

Senzatela provided a tease of his good side Friday when he forced a couple of double plays in the first three innings, and only the speed of the D-backs’ Eduardo Escobar prevented a double play to end the fourth. But the next hitter, Walker, did damage with the first of his two homers.

A 2-0 deficit is dicey against D-backs starter Zack Greinke, who would strike out nine in seven scoreless innings. The Rockies’ only threat came with runners at second and third in the third, and ended when David Dahl struck out looking. Afterward, even while praising Greinke’s working of the corners and the use of his changeup, Dahl said, “That was a ball.”

The last 14 times Greinke has faced the Rockies, he’s gone 6-3 with a 3.08 ERA, though Colorado won all five no-decisions. The idea is to keep the score close, then win against the bullpen. Senzatela even did his part to drive up Greinke’s pitch count with a nine-pitch at-bat before striking out to end the top of the fifth.

Then Senzatela unraveled in the bottom of the frame by giving up a Jake Lamb single, walking Nick Ahmed -- which Black called “the backbreaker” because it came after an 0-2 count -- and serving up Alex Avila’s two-run double. Senzatela had beaten him with two breaking balls, but the third one did not dive low enough. A hit and a walk later, and Senzatela was gone.

“In the fourth inning, I left the ball up [to Walker], and in the fifth everything was kind of the same,” Senzatela said.