PITTSBURGH -- J.A. Happ didn't factor into the Pittsburgh Pirates' plans at the trade deadline. But an injury to All-Star A.J. Burnett forced them to acquire him as emergency rotation depth at a time the Seattle Mariners were on the verge of removing him from the starting rotation.

After Happ gave up four runs in 4 1/3 innings in his debut, the left-hander has delivered two solid outings since that resulted in victories. Wednesday, he shut out the National League's highest-scoring offense for six innings as the Pirates beat the Arizona Diamondbacks 4-1.

"He had some challenges in the second half," Pittsburgh manager Clint Hurdle said. "He seems to have figured some things out and gotten to a better place."

Happ (1-1) gave up two hits, walked two and struck out three.

"He just pitched in really effectively," Arizona manager Chip Hale said. "He was able to get guys looking in there then use the ball away."

Pittsburgh took two out of three games from Arizona and the Pirates lead the National League wild-card race by 3.5 games.

Both of Happ's walks came in the second, when he put center fielder A.J. Pollock and catcher Jarrod Saltalamacchia on leading off the inning. Pollock advanced to third but was stranded when right fielder Yasmany Tomas grounded out.

Arizona did not advance another runner past first base until the ninth.

"We were patient there," Hale said. "Guys did a good job. But that was it. It wasn't real pretty offensively until late."

Diamondbacks left-hander Robbie Ray also lasted six innings but his outing was marred by a three-run second.

Ray (3-9) allowed three runs and seven hits. He walked two and struck out five.

The left-hander has lost his last five decisions and the Diamondbacks have lost in his last four starts.

Ray hit shortstop Jung Ho Kang, who advanced to third on catcher Francisco Cervelli's single and scored on a wild pitch.

Second baseman Sean Rodriguez hit a single to score Cervelli and right fielder Gregory Polanco hit an RBI double to left-center for a 3-0 lead.

Ray pinned his fastball command as the culprit for the fateful inning, but that he also got away from his identity as a pitcher.

"I was trying to nibble at the corners and that's just not who I am," Ray said.

The Pirates added an insurance run in the eighth when Arizona right-hander Zack Godley walked first baseman Pedro Alvarez with the bases loaded.

Rodriguez finished with three hits and an RBI. Center fielder Andrew McCutchen and left fielder Starling Marte added two hits apiece.

"Definitely starting to feel more comfortable," Rodriguez said. "Sometimes it could be the timing. Sometimes it could be other things."

Right-hander Joakim Soria and left-hander Tony Watson worked shutout innings before right-hander Mark Melancon's services were required despite a four-run lead. Left-hander Antonio Bastardo gave up a walk and hit and Melancon was called out of the bullpen.

First baseman Paul Goldschmidt hit an RBI single to left to cut Pittsburgh's lead to 4-1. Melancon retired the next three batters to record his 38th save.

NOTES: Pittsburgh added RHP Josh Wall to the active roster after the bullpen was taxed in the Pirates' 9-8, 15-inning win Tuesday. SS Pedro Florimon, who tripled home the walk-off run, was designated for assignment. ... Arizona recalled RHP Zack Godley from Double-A Mobile and optioned RHP Chase Anderson to Triple-A Reno. Anderson has given up 12 runs over 9 2/3 innings in his last two starts. ... Pittsburgh CF Andrew McCutchen was elected to the Arizona Fall League Hall of Fame on Wednesday.