Correia (9-6) won his seventh straight decision, a streak that covers eight starts and 50 days. Weathering a couple of significant jams, the righty allowed four runs, three of them earned, and walked three while striking out five.
"Correia going out there as little as he's pitched was absolutely enormous," Walker said. "I don't know if people realize how difficult that is, the tough spot he's been in."
And on the subject of tough spots, lefty Tony Watson had to leave the bases loaded with D-backs in the seventh, and Chad Qualls had to strand the tying run in the eighth. When Joel Hanrahan entered in the ninth, so did calm -- he fanned the side for save No. 33.
It was both a tidy save and a cleanup job for Hanrahan, who nailed down a game in which the Pirates committed four errors.
"You never like to say you're winning ugly, but that was about as ugly as it gets," Walker said. "The wet weather on top of it, we're sloppy defensively ... We still felt pretty good to get into the ninth with Joel. That was the main thing -- get the ball in Joel's hand. At that point we're feeling pretty good about our chances."
So the extraordinary and the ordinary merged to bring the Pirates within 2 1/2 games of the National League Central-leading Reds, who are on a four-game losing streak begun by A.J. Burnett's two-hit pitching on Sunday.
The ordinary was Walker's two-run double in the fifth. That gave him 41 RBIs on 15 career hits with the bases loaded, situations in which he is a .500 hitter.
It marked the second time in seven games that Walker drove in five runs. Following a five-RBI game a week ago in Chicago that included a grand slam, he explained his ownership of bases-loaded situations.
"I thrive when there are runners in scoring position," Walker said then, "and if it isn't a two-out situation, you know you have the pitcher in the palm of your hand. He's got to make pitches. For some reason I feel I lock it in a tiny bit more. You know guys will have to come at you. I hit pretty well with bases loaded; I tighten it down a little bit."
At the outset, Correia was not encouraging. Arizona's first four batters all produced: Stephen Drew doubled, Willie Bloomquist bunted for a hit, Chris Johnson singled for a run and Paul Goldschmidt plated Bloomquist with a sac fly. It was quickly 2-0, and the emergency for which left-hander Jeff Locke had been recalled seemed near.
Then Correia put his foot down, retiring the next eight men and 12 of 14.
"I was proud of his effort tonight," said the man who had sent Correia to the 'pen, manager Clint Hurdle. "He competed very well, and gave us a chance to win the ballgame."
"It's always nice to please the people who make the decisions on when you get to play and when you don't," Correia said.
If Correia needed a fresh slate after his rough top of the first, Walker was more than happy to apply the eraser. Walker dotted a two-out rally in the first against Ian Kennedy, following singles by Andrew McCutchen and Garrett Jones with his 13th homer. That is a new career high for the local kid, who wound up each of his first full seasons with a dozen.
"I got ahead of guys but didn't finish them off after that," Kennedy said. "Walker, I pretty much hung a changeup to him. I just didn't execute at all tonight. It's frustrating. We're trying to stay in this NL West race, and to pitch like that is not acceptable."
"It was definitely nice to be back on top that quick," Correia said. "I didn't feel that bad in the first, although there was a little bit of rust. But after that I was decent; in the second I was a little more aggressive."
Marte led off the third by making it 4-2 with his fourth homer, a shot into the right-center grandstand.
As someone not equipped to blow people away, Correia depends on pinpoint control, and he briefly misplaced it in the fifth. He also misplaced eight pitches to Gerardo Parra and Drew, walking both around Kennedy's sacrifice bunt and paying for it on Bloomquist's RBI double. When Pedro Alvarez botched Goldschmidt's two-out grounder, Drew scored from third to make it 4-4.
That was Alvarez's 18th error of the season, a new personal high (he had 17 as a 2010 rookie) and the most in the Majors. Arizona's Johnson is next, with 15.