Walker's final line was four runs, three earned, over six innings on eight hits - he walked as many as he struck out, with three of each.
The Pirates are showing signs they're ready to break out offensively, scoring four runs in each of their last two games after doing so just once in their previous nine contests.
The win was overshadowed by an injury to catcher Chris Iannetta.
The pitch got away from Pirates reliever Johnny Barbato, and caught Iannetta flush in the mush.
Iannetta went to a local hospital immediately.
The incident cast a pall over what was an offensive explosion for Arizona, which has won three straight.
Lovullo told the media following the game that Iannetta had been up and walking and everything was fine with him. "Everything was OK", Lovullo said. After Jordy Mercer was walked intentionally, Williams reached when second baseman Brandon Drury's error on a routine grounder allowed Freese to score. Drury hit a three-run homer during the burst.
"There's a strategy to pitching in and there's a need for pitching in", Lovullo said, "and by no means do I think anybody tried to hit Chris Iannetta in the face yesterday". Catching way too much of the plate. They scored four runs on Friday, the first time that has happened since May 5. "Not when the other team has (11)". Arizona Diamondbacks' Patrick Corbin (46) scores a run on a triple by A.J. Pollock as Pittsburgh Pirates' Chris Stewart, right, waits for a late throw during the third inning of a baseball game Friday, May 12, 2017, in Phoe.
Outfielder Gregory Polanco has enjoyed success against the Diamondbacks. Arizona attempted to rally late from a 4-1 deficit and extend its winning streak to four games but fell just short. Williams has made six relief appearances as well.
Arizona raced out to the lead in the National League West at the start of the season, but has dropped to third place 2 games behind the first place Colorado Rockies and a half game behind the second place Los Angeles Dodgers.
This time, Trevor Williams looked like he belonged in the Pittsburgh Pirates' rotation.
Pittsburgh took a 2-1 lead in the fourth despite getting only one ball out of the infield.
The Diamondbacks counter with right-hander Taijuan Walker (3-2, 3.83). That this worked out was a pleasant surprise after the Pirates' bats went silent for several innings and a series of oddities that seemed destined to end in a loss.
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