Maholm surrendered four consecutive run-scoring hits with two out in the second. He was chased an inning later after opposing pitcher Esmil Rogers ripped a two-out double to score Ian Stewart, who had reached base on Maholm's error.
"[Maholm] just never really got into any kind of rhythm," Pirates manager John Russell said. "[He had] trouble putting hitters away when he got ahead of them, and it was just one of those starts. It looked like he was going to be all right, and then it just snowballed on him."
Maholm also gave up a two-run homer to Carlos Gonzalez in the first.
With his sinkerball off the mark, Maholm threw 82 pitches over 2 2/3 innings, giving up eight runs -- six earned -- on seven hits.
"I felt great. I guess overthrowing too quick, pulling stuff," Maholm said. "It seemed like every time I threw a good pitch they'd foul it off, then I'd make a mistake and leave one over the middle."
Maholm had not allowed more than four runs in a single outing through his first 14 starts, when he was 4-5 with a 3.77 ERA and the ace of an otherwise disappointing staff.
But the southpaw has now surrendered at least five runs in four of his last nine starts, a stretch that started with a one-inning, seven run (five earned) performance on June 23 at Texas.
Though longer, Sunday's start had little more to offer. Even his two-run first inning took 32 pitches.
The positive signs Maholm has shown during this stretch have made it all the more puzzling. He followed that Texas start with eight innings of one-run ball against the Cubs, and he pitched a complete-game shutout against Houston on July 18 -- his first start after the All-Star break.
In his four starts since, however, Maholm is just 1-3 with a 9.90 ERA.
"Just going out there and doing it," Maholm said of the key to getting back on track. "I'm going to do everything possible to make sure that this is the last one of these like this, and go out there and do it.
"Not talk about it, not try and dwell on it too much. Just go pitch like I normally do."
Less perplexing on Sunday was the continued displays of dominance from Gonzalez and Troy Tulowitzki, Colorado's Nos. 3 and 4 hitters, respectively.
Still, there was no getting around the duo's simply phenomenal performance this weekend. Gonzalez and Tulowitzki finished the four-game series hitting a combined .514 (18-for-35) with two home runs and nine RBIs.
In their seven games against the Pirates the past two weeks, the two batted a combined .439 (25-for-57) with four home runs and 13 RBIs, capped by Gonzalez's 4-for-5 afternoon in the finale.
"I don't really have words to say for you guys to write," Rockies manager Jim Tracy said of Gonzalez, who has now homered eight times in his last 11 games. "You guys go ahead and do it."
Daniel McCutchen relieved Maholm and immediately gave up an RBI ground-rule double to Dexter Fowler before recovering nicely. He pitched 4 1/3 scoreless innings. Chris Resop and Chan Ho Park each added a scoreless inning of relief, giving the Pirates' bullpen 6 1/3 scoreless innings on the afternoon.
"Anytime your bullpen goes out there and gives you shutout innings, whether it's one, two or eight, it's always good," Resop said.
McCutchen also reached base when hit by a pitch in the left shoulder in the sixth inning, and he stole second afterward. It marked the first stolen base by a Pirates pitcher since May 17, 2006, when Oliver Perez recorded one against the Reds.
Rogers, however, stole the offensive thunder from the pitching standpoint, hitting his second double in the sixth.
Ronny Cedeno was one of three Pirates with two hits, including an RBI single in the second that scored Ryan Doumit and got Pittsburgh on the board after the seemingly eternal top half of the inning. Cedeno added a double in the fourth.
Garrett Jones reached on an error in the fifth, scoring Andrew McCutchen, and Neil Walker and Pedro Alvarez added RBI singles in the fifth to cut the deficit to four.
"It wasn't so much disappointing as we knew we had a mountain to climb today because we got down big," Russell said. "So the guys weren't really worried about it and weren't feeling low because of what happened [Saturday] night. They're still pretty up from that and they started to peck away. That's what they were talking about every inning -- keep pushing, keep driving."
A day after staring defeat down to its last strike before prevailing, the Pirates could not overcome an early 8-1 deficit.
"When you can't get a guy out with two outs and they score an extra six runs," Maholm said, "that's what it boils down to."