Zac Gallen returns from a 30-day absence when the Arizona Diamondbacks face the Oakland Athletics on Saturday in the middle contest of a three-game set at Phoenix.

Gallen has been sidelined since injuring his right hamstring against the New York Mets on May 30. He said he sustained the injury on his fifth pitch of the game. Gallen exited one pitch later.

When Gallen takes the mound, he will be looking to help Arizona rebound from a 9-4 loss in Friday night's series opener.

The right-hander ramped up his progress this week with a 67-pitch effort in a simulated game on Monday and a bullpen session three days later.

Manager Torey Lovullo hinted about Gallen's return before Friday's game.

"It's probably the worst kept secret in all of Major League Baseball. He should be very ready and don't be surprised in the next 24 hours he's our starting pitcher," said, Lovullo, who made the official announcement after the game.

The Diamondbacks are certainly happy to get their ace back. In the previous six games, the pitching staff has been hammered for 50 runs and 72 hits. The opposing team has 14 hits three times during the stretch and games of 13 and 11.

Gallen (5-4, 3.12 ERA) placed third in National League Cy Young balloting last season after recording career highs for victories (17), strikeouts (220) and innings pitched (210). He also was the NL's starting pitcher in the All-Star Game.

The 28-year-old Gallen hasn't found the same groove this season and lost four of six starts prior to the outing in which he was injured against the Mets.

Gallen has a 1.64 ERA in two career starts, both going as no-decisions, against Oakland. Aledmys Diaz is 1-for-6 against Gallen.

The Athletics brought their power bats and slugged four homers in the series opener.

They halted a five-game overall losing streak and an 11-game road skid. Their previous road win came against the Atlanta Braves on June 1.

Tyler Soderstrom hit a tying homer in the eighth inning. Brent Rooker, Shea Langeliers and Daz Cameron all smacked homers in the ninth inning.

"The offense swung the bats well," Oakland manager Mark Kotsay said. "Overall, it was a great game."

Light-hitting Zack Gelof had three hits, including the go-ahead triple in the eighth inning.

"It was a great night for Zack," Kotsay said. "He's been working very hard. The month of June has been a lot better for him than April and May, and he's finishing up this month very strongly."

Gelof is batting .256 with five homers in June. He has raised his average 26 points to .205.

"All around, we put it together," Gelof said of Friday's victory. "It just feels good to win on the road."

The victory was just Oakland's fourth in its past 19 overall games, and it continued a bad stretch for the Diamondbacks.

"We've got to pitch better," Lovullo said afterward. "You can't make assumptions because the Oakland A's are here that we're going to beat them three games. That's a well-run team. They've got a good manager with young players that are very enthusiastic."

Left-hander Hogan Harris (1-1, 2.72) will start for the Athletics on Saturday.

Harris, 27, lost to the Minnesota Twins on Sunday when he gave up three runs and five hits in six innings.

In his previous turn, Harris picked up his first win of the season by holding the Kansas City Royals to three runs (one earned) and four hits over five innings.

Harris has never faced the Diamondbacks.

--Field Level Media