Two of Baltimore’s top prospects in 2015 led their team to victory Friday.

That team just wasn’t the Orioles.

Arizona Diamondbacks pitcher Zach Davies and first baseman Christian Walker handed Baltimore a 4-2 loss to open the weekend series at Chase Field.

Davies, who spent the first four years of his professional career in the Orioles’ minor league system, entered the game as one of the least effective pitchers in the major leagues. But he shut down his former organization, twirling six innings of one-run ball for just his second win of the season.

Walker, a first baseman the Orioles selected in the fourth round of the 2012 draft, hit a two-run homer in the sixth inning to provide the difference. Walker debuted with the Orioles in 2014 but was designated for assignment before the 2017 season. In seven years with the Diamondbacks, he’s posted a .799 OPS. After hitting 36 homers last year, Walker smashed his 29th of the season Friday.

In 2015, Walker and Davies were ranked by MLB Pipeline as the Orioles’ Nos. 3 and 4 prospects, behind pitchers Dylan Bundy and Hunter Harvey.

After scoring a run in the first inning, the Orioles’ bats couldn’t muster another until the eighth inning. Both runs scored on two-out hits from Ryan O’Hearn to score Gunnar Henderson. But Austin Hays, representing the tying run in the eighth, struck out to end the inning. After a leadoff single from Cedric Mullins in the ninth, the Orioles couldn’t mount a comeback off closer Paul Sewald.

Davies, a right-hander selected by the Orioles in the 26th round of the 2011 draft, entered the series opener 1-5 with a 6.93 ERA in 13 starts. The only MLB pitchers with at least 60 innings and an ERA worse than Davies’ entering Friday were St. Louis’ Adam Wainwright and Detroit’s Joey Wentz.

Five times this season opposing teams scored at least five runs off Davies, who the Orioles traded to Milwaukee at the 2015 deadline for outfielder Gerardo Parra. Only once this season had the 30-year-old pitched at least six innings and allowed no more than one run. In nine big league seasons with the Brewers, San Diego Padres, Chicago Cubs and Diamondbacks, Davies owns a 4.29 ERA.

“Well, I just thought we expanded the zone too much on him,” manager Brandon Hyde said. “Our approach tonight going in was outstanding and we didn’t really follow through in the game. We just didn’t take very many good at-bats. Give him credit, but we’ve got to score more than two runs to be able to win these games.”

Henderson and O’Hearn both went 2-for-4 with a double, while the rest of the Orioles’ lineup managed just four hits in 26 at-bats. Baltimore went 2-for-11 with runners in scoring position. Batters were hitting .287 off Davies entering Friday.

“We’ve got to do a lot more offensively,” Hyde said. “We haven’t been swinging the bat very well. We’ve got to do a lot more offensively to keep the line moving and score more runs.”

Arizona, meanwhile, scored its four runs on two big swings off Orioles starter Cole Irvin. After Baltimore took a 1-0 lead on O’Hearn’s RBI single in the first, Irvin gave the lead right back, allowing a two-run homer to Lourdes Gurriel Jr. on just the fourth pitch of the left-hander’s night. Gurriel clobbered the hung changeup 403 feet to left field.

Irvin, the Orioles’ sixth starter in the six-man rotation it adjusted to last month, retired 15 of the next 18 batters he faced to begin the sixth inning cruising. But Tommy Pham led off the inning with a double to left field, and Walker gave the Diamondbacks (70-65) all the offense they would need.

“Aside from those two two-run homers, he did OK,” Hyde said about Irvin, who allowed eight hits in 5 2/3 innings before relievers Joey Krehbiel, Shintaro Fujinami and Cionel Pérez combined for 2 1/3 scoreless.

Since rejoining the Orioles in June, Irvin has a 3.65 ERA in 56 2/3 innings. But he’s completed six innings in just two of his 12 starts this season, and he’s surrendered four runs in each of his previous two.

“I felt like I’ve been good,” Irvin said about his recent performance. “Today, I’m a little disappointed. Ultimately, just because I gave up two homers and kind of let the game get away from me, but all in all, I felt I’ve been throwing the ball well.”

The main bright spot of the evening for Baltimore was the stellar defense played by Henderson. The rookie made two outstanding plays at shortstop for double plays. In the sixth, he fielded a ground ball on the second base side of the bag and was still able to touch the base and throw out speedster Corbin Carroll at first.

But his most impressive play — one of the best defensive highlights by an Oriole this season — came two innings earlier when the 22-year-old ranged 106 feet down the left field line to catch a popup over his shoulders and then nab Carroll with a 90.2 mph throw to home plate, according to Statcast tracking data. Henderson and Carroll are the front-runners to win the Rookie of the Year awards for their respective leagues.

“He’s one of the best rookies in the game right now,” said Irvin, the beneficiary of both of Henderson’s double plays. “He’s just exciting to watch. He brings the energy, plays hard.”

“I felt like it was a pretty good one, but would’ve loved to win the game,” Henderson said. “I felt like it was a good defensive game and was glad to help keep the team in the game.”

Baltimore falls to 83-51 with the loss, but the Tampa Bay Rays didn’t gain ground. The Cleveland Guardians came back from down 2-0 to beat the Rays, 3-2. The Orioles are 1 1/2 games up on Tampa Bay atop the American League standings.

Around the horn

• Mid-Atlantic Sports Network broadcaster and Hall of Famer Jim Palmer returned to the booth Friday for his first game since he was hospitalized with COVID-19 in early August.
• Triple-A Norfolk catcher Maverick Handley was removed from Friday’s game after colliding with another player, the Orioles said. Last week, Tides catcher Anthony Bemboom and High-A Aberdeen backstop Samuel Basallo were both placed on the concussion injured list.

Orioles at Diamondbacks

Saturday, 8:10 p.m.

TV: MASN2

Radio: 97.9 FM, 101.5 FM, 1090 AM

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