Beckham extended his hitting streak to 12 games to begin his Orioles career and scored three runs. The Orioles pounded out a season high-tying 20 hits, matching their total in a 13-inning game on May 16 at Detroit.
Adam Jones went 3-for-5 with a double and three RBIs, and Joey Rickard went 3-for-4 with a double and three runs. He was also hit by a pitch.
Every starter except catcher Welington Castillo had at least one hit for the Orioles (58-59).
Bundy (12-8) won his fourth straight game, matching his career high set earlier this season. He allowed three runs and seven hits in six innings with three walks. He struck out 10 for the second straight start, making good use again of a sharp slider.
A's left-hander Sean Manaea (8-7) had the shortest start of his career, allowing six runs and six hits in one-third of an inning. The only out came on a relay to home plate.
Manaea walked one and didn't strike out a batter. He had his third straight rough start and the velocity on his fastball was down to 90-91 mph again instead of his typical 93.
Khris Davis hit his 32nd home run of the season, a two-run shot, and rookie Matt Olson hit his sixth blast, a solo home run, for Oakland.
Center fielder Boog Powell made his A's debut and went 1-for-4 with a walk, three strikeouts, a run and an outfield assist. Powell had been slated to play Friday, but he was a late scratch because of an upper respiratory infection and an asthma attack that sent him to the emergency room at a local hospital.
The Orioles struck quickly, scoring seven times in the first inning.
Baltimore had eight hits in the inning, including doubles by Manny Machado, Jones, Mark Trumbo and Beckham. The Orioles sent 11 batters to the plate.
Beckham led off with a walk and scored on Machado's double off the left-center field wall. Jonathan Schoop lined a single to right, moving Machado to third. Jones drove in Machado with a double to left, but Schoop was thrown out at the plate on a relay from Davis in left to shortstop Marcus Semien to catcher Bruce Maxwell.
Trey Mancini made it 3-0 with an RBI single, driving in Jones, and moved to third on Trumbo's double. Chris Davis grounded an RBI single to right, making it 4-0 and ending Manaea's night as Michael Brady took over.
Castillo brought Trumbo home when he grounded into a fielder's choice. Rickard singled, and Beckham increased Baltimore's lead to 7-0 with a double to left.
Oakland cut the deficit to 7-2 in the bottom of the inning when Powell led off with a walk and Khris Davis launched a two-run homer with two outs. Olson led off the second with a solo home run into the right field seats.
Baltimore answered with two runs in the fourth. After Rickard was hit by a pitch and moved to third on Beckham's double, Jones lined a two-run single to center.
NOTES: Orioles RHP Ubaldo Jimenez (sore right calf) came out of his start against Oakland on Friday night with one out after getting hit by a comebacker on his right calf, but Orioles manager Buck Showalter said he expects him to make his next start. "He'll be fine," Showalter said. "The biggest problem he had, that's the same place he got hit in Minnesota (on July 9)." ... A's OF Jake Smolinski (right shoulder surgery) began a rehab assignment with Class A Stockton on Saturday and served as the designated hitter. Smolinski's throwing shoulder is still not healthy enough for game action. He has been on the disabled list since March 30. ... A's RHP Liam Hendriks made his team-high 52nd relief appearance and pitched 1 1/3 scoreless innings.