PHOENIX — If the Mets’ fade into oblivion continues, if they fail to reach the playoffs and waste a season of promise, the blame will lie partially with their incompetence against the Diamondbacks.

Mired in last place? Long out of the playoff chase? Playing for nothing else but pride? None of that has mattered to the Mets, whose latest humbling came in Monday night’s 10-6 loss to begin a 10-game road trip.

Fresh off winning consecutive games for the first time in more than a month, the Mets arrived in the desert looking to make it three in a row. But even against the lowly Diamondbacks, that modest goal proved too ambitious.

Mets starter Bartolo Colon made history at the plate, drawing a walk for the first time in his 500th major-league game when Diamondbacks lefty Robbie Ray missed high and tight with a 94-mph fastball. Colon had gone 281 plate appearances spread over 19 seasons without a base on balls — the longest streak ever in the big leagues, according to ESPN Stats and Info.

“That surprised me as well,” Colon said through a translator. “I don’t know why that pitcher didn’t strike me out. He could have. I really couldn’t do much more at that point.”

But the 43-year-old Colon is paid to pitch, not hit. And in his primary vocation, he endured a rough night, allowing five runs (two earned) and nine hits. An error by third baseman T.J. Rivera in the first opened the door for three unearned runs.

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Colon was done after four innings. “He really didn’t have his good location going,” Terry Collins said.

After sweeping a three-game series at Citi Field last week, the Diamondbacks continued their onslaught against the Mets by pounding 16 hits. Four came off the bat of Welington Castillo, equalling a career high. Paul Goldschmidt fell a home run shy of the cycle.

Travis d’Arnaud collected three hits and Jose Reyes added a pair of RBI singles for the Mets, who had 12 hits and drew five walks. But they were hardly enough to mask another night of struggles for a lineup that won’t get back Yoenis Cespedes or Asdrubal Cabrera until Friday at the earliest.

Curtis Granderson, mired in a brutal slump, went 1-for-5, with his only hit a leadoff single in the seventh with the Mets trailing by six runs. Before that, he had stranded five baserunners, continuing his season-long struggles with runners in scoring position. He entered play hitting .138 since July 27.

Even with the loss, the Mets are three games out of the second wild-card spot in the National League, behind the Marlins, Cardinals and Pirates. And like the Mets, all three have their warts.

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The Mets’ failures with runners in scoring position have helped usher this season to the brink. They began the day hitting .204, the worst in baseball. Though they finished 3-for-10, those issues presented themselves again.

Consider the seventh. Down six runs, the Mets loaded the bases with none out. They scored three runs but missed an opportunity to climb all the way back. Wilmer Flores worked a bases-loaded walk and T.J. Rivera and Ty Kelly lifted consecutive sacrifice flies. But d’Arnaud struck out to end the threat.

Yasmany Tomas ended any faint hopes of a comeback with his 22nd homer, a two-run shot in the eighth off Hansel Robles.

The Mets have not won three straight since a five-game winning streak from June 30 to July 4.

In last week’s three-game sweep, the Mets scored only five runs against the Diamondbacks, who began play with an NL-worst 5.09 ERA. In Monday’s series opener, the Mets eclipsed that total. But it wasn’t enough on a night in which the bullpen surrendered five runs.

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“People have hit them,” Collins said. “We haven’t been hitting. So we’ve had a tough time scoring.”