PHOENIX — It was bound to happen eventually. Sooner or later, and probably sooner, a Phillies starting pitcher was going to throw a dud.

Vince Velasquez, come on down.

Nearly two months after the last time he got roughed up — nine games after a Phillies starter last allowed more than three runs in a game — Velasquez lasted just  four innings in  a 6-0 loss to the Arizona Diamondbacks on Wednesday in a series finale at Chase Field.

"Just a terrible display of executing my secondary pitches," Velasquez said, succinctly.

Velasquez didn't have his best stuff, to be sure. He gave up four runs on six hits and two walks, hit a batter, and lacked the usual sizzle on his fastball. His heater averaged 93 mph, according to Statcast, a tick below his season average of 94.1 mph but a dip that manager Gabe Kapler attributed to pitch selection (more sinkers, fewer four-seamers) rather than other, potentially sinister factors.

But for a third consecutive game, the Phillies offense dried up in the desert. Diamondbacks starter Patrick Corbin held them to four hits in 7 1/3 innings. Roman Quinn's pinch-hit double in the fifth inning marked the Phillies' only extra-base hit.

After scoring 23 runs in a four-game sweep of the Miami Marlins at home last week, the Phillies produced only seven runs in 32 innings against the Diamondbacks. And four of those runs came in the seventh inning Tuesday night after starter Nick Pivetta had exited with a 1-0 lead.

The point is, Velasquez would have needed to be nearly perfect for the Phillies to pull this one out. And the starters can't be so perfect all the time.

As a result, the Phillies dropped two of three games against the Diamondbacks, a playoff contender out of the National League West. Muted bats aside, though, they still might have won the series if they hadn't blown a two-run lead in the ninth inning of the series opener Monday night and lost in 14 innings before coming back to beat Diamondbacks ace Zack Greinke in the middle game.

"You're going to go into a city like Phoenix against a very good team and sometimes you're going to win the series. And there are going to be other times where they just play better," Kapler said. "Over the course of this series, they just played better than us. We ran into three quality [starting] pitchers and a team with a very good bullpen. It's part of baseball."

For two months, Velasquez has been among the best starters in baseball. He entered with a 2.14 ERA since June 14, including a 1.39 mark in his last six starts. And beyond the numbers, he's had the look and the stuff of an emerging ace.

Known for his blazing fastball, Velasquez tried instead to run his sinker in on the hands of Arizona's righthanded hitters. As a result, he appeared to lack his typical power and didn't generate quite as many swings and misses as usual.

If anything, though, Velasquez seemed to be more disappointed in his sequencing than with his actual pitch mix.

"Probably if I used my secondary pitches a lot more I probably would've got a lot more swings and misses," Velasquez said. "It doesn't matter if I was throwing 96, 97. If I used [his offspeed stuff] in the right count they would have been late on my fastballs."

Velasquez flirted with trouble early, overcoming a two-out single in the first inning and back-to-back two-out walks in front of Corbin in the second.

But the Diamondbacks finally got to him for three runs in the third. Jon Jay sliced a leadoff double, Paul Goldschmidt got hit by a pitch, and David Peralta lined a two-run triple into the right-field corner. Two batters later, Peralta scored on a sacrifice fly by Eduardo Escobar.

The Diamondbacks continued to hit the ball hard in the fourth inning, tacking on a run on back-to-back singles by Ketel Marte and Alex Avila followed by Corbin's double-play grounder.

"I'm kind of kicking myself in the butt because I know I can execute those [secondary] pitches," Velasquez said. "Sometimes you have a solid warm-up before and you have that conviction in those pitches, and sometimes they just don't work."