FREDERICK — The Orioles hope right-hander Yovani Gallardo can provide the team's struggling starting rotation — a unit that had a 4.80 ERA over the past week heading into Thursday night — a much-needed boost after making his two scheduled minor league rehabilitation starts.

Gallardo made his first rehab start Thursday for High-A Frederick. It was his first game since leaving his most recent Orioles start in Kansas City after two innings and heading to the disabled list nearly six weeks ago, and his results were less important than the way his right shoulder felt after the outing.

He was scheduled for four innings in Thursday's opening game of a doubleheader against the Potomac Nationals, but a 26-pitch first inning prevented Gallardo from achieving that.

Instead, it took just three innings for Gallardo to reach 59 pitches (43 strikes). He allowed three runs on seven hits, striking out four and walking two. He allowed two runs in the first inning, when five of the first seven batters he faced reached base on four singles and a walk. But the Carolina League hitters didn't draw much hard contact against Gallardo.

“I think just getting back out there is definitely a step forward,” said Gallardo, who had never gone on the DL before for an arm-related injury. “It's always tough with the shoulder issue. You really had to take it one step at a time. You don't want to get too far ahead of yourself, but it feels good. I was able to move the ball around, just trying to mix all my pitches. Pretty good stuff. I'm looking forward to the next one, wherever it might be.”

Gallardo allowed singles to four of the first five hitters he faced. Potomac added a run in the third off Gallardo on a two-out single by David Masters.

Gallardo is set to make his next rehab assignment Tuesday — he could make a second start for Frederick or pitch for Triple-A Norfolk — and barring a setback, the Orioles have penciled in a June 12 return for the finale of the team's three-game series in Toronto.

“I definitely feel good,” Gallardo said. “I've been feeling great ever since I started throwing.”

The Orioles forfeited their first-round pick in next week's draft to sign Gallardo — an initial three-year deal was restructured to a two-year, $22 million contract after concerns over his shoulder emerged in his club physical — and Gallardo landed on the DL after just four starts.

Duensing joins bullpen: Veteran Brian Duensing was recalled from Norfolk just 10 days after signing a minor league contract with the Orioles and will be a left-handed middle-relief specialist.

Duensing, who spent seven years in the Minnesota Twins organization before signing as a free agent with the Kansas City Royals at the start of spring training, never pitched at the major league level with the Royals. He opted out of his minor league contract May 15 after going 1-0 with a 3.10 ERA and two saves in 12 appearances at Triple-A Omaha. With the Tides, he made three scoreless appearances and struck out six in three innings.

Though Duensing made 61 starts during his career with the Twins, Orioles manager Buck Showalter said definitively that Duensing will not be a candidate to fill the void created in the Orioles rotation when Mike Wright was sent back to Norfolk.

Duensing made his Orioles debut in a ninth-inning mop-up appearance that didn't go well. Four of the seven batters he faced reached base and the Red Sox scored two runs, though it didn't matter much at that point.

McFarland happy to be back: Duensing arrived the day after left-hander T.J. McFarland rejoined the major league club, leaving room to speculate that McFarland, who pitched well as a starter at Norfolk, might temporarily fill the slot left open by Wright.

McFarland doesn't know, and he's happy just to be back in the major leagues after stretching out as a starting pitcher at Norfolk.

“I enjoyed it,” he said of starting. “I was able to kind of mix up my pitches a lot more. I was able to stretch out and was able to get up to 72/3 [innings], which was nice, so I'm definitely happy to be back here.”

Around the horn: Left fielder Hyun Soo Kim was back in the starting lineup Thursday, batting second. He has been in the lineup eight of the past nine games. He singled in his first at-bat Thursday.

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Schmuck reported from Baltimore.