The loss also gives the A's 13 losses in their last 17 games, and this most recent one made Dallas Braden's best outing of his career all for naught.
Braden lasted a career-high seven innings, allowing just one run and surrendering just four hits, but picked up the loss.
"He did a real nice job," Geren said. "He had a lot of swings and misses and when he got in trouble, he got out of it."
It was Braden's fifth straight decision that ended up in a loss, which is the longest streak by an A's pitcher this season; though this time, he deserved a better fate.
Braden has certainly thrived against the Orioles this year, compiling an ERA of 1.39 in 13 innings against Baltimore, while posting a 7.23 mark against the rest of the league.
"Getting ahead early was a major factor for me," Braden said. "I think that anytime someone does well, it gives them a boost of confidence. But I am not worried about myself. I want to be able to help the team do what we want as a collective unit, and that's win."
In an April 24 start against the Orioles, which was his Major League debut, he lasted six innings and gave up only one run on three hits.
The A's offense, unfortunately, couldn't put together a repeat performance of Saturday night's game when they had 11 hits. They followed that up on Sunday with only two.
The last time Braden faced the Orioles, he was opposed by Jeremy Guthrie, and even though the A's scored only two runs (one earned) against him, they still fared better during that go around than they did this time.
"Last time, we got him for a couple early and beat him," Geren said. "But it just didn't happen today."
The A's saw why Guthrie has developed into one of the best pitchers in the American League, entering Sunday's game in the top five in ERA. He left the game with that being the case as well.
Guthrie shut down the A's over seven innings, allowed just two hits and struck out six batters.
"He was lights out," Geren said. "He was working the corners all day and [it] was very difficult to put a hard-hit ball into play. You have to give credit where credit is due."
The only blip on the radar for Braden wound up being the only run Guthrie would need as the Orioles finally got on the board in the sixth inning.
Brian Roberts drew a leadoff walk to start the inning and Kevin Millar came through with a two-out single to bring him home.
"The guy that scores is a walk, and that kind of [stinks]," Braden said.
Braden was able to pitch out of a jam in the first inning. After allowing the first two batters of the game to reach he struck out the side, including two batters looking.
"You don't want to give them an early run and start fast," Braden said. "I was trying to give myself a chance to stay in the game."
Guthrie, on the other hand, was so sharp for the Orioles that he did not allow an Oakland baserunner to reach second base. The A's had just five baserunners the entire game, drawing three walks on top of the two hits.
Even after Guthrie departed, the A's only got one runner on base and still couldn't get a man into scoring position.
The A's split the season series with the Orioles with each team winning four games, marking the first time since 1997 that Oakland has been unable to take the season series from the Birds.