Jason Hammel's second start for the A's will be his first start against the O's, his former club, since 2008.
Hammel was shipped to Oakland from the Cubs earlier this month in the blockbuster trade that also included Jeff Samardzija. His first start came before the All-Star break, when he gave up three runs (two earned) over five innings against the Giants.
He'll be facing the Orioles, a team he pitched for in 2012 and '13 before heading to Chicago. Hammel has a 6.68 ERA and 0-4 record against a Baltimore team that manager Bob Melvin has spoken highly of this season.
"They do a lot of things right," Melvin said. "They definitely have strengths and also some guys that probably haven't gotten as hot as you'd expect. There's a reason they're in first place."
After the A's series-opening, 5-4 win on Friday, Hammel will look to outduel left-hander Wei-Yin Chen, who has a 9-3 record.
Chen's last outing before the All-Star break was against the Nationals in Baltimore, and he allowed eight hits and three earned runs in 5 2/3 innings, which was enough for the win.
Chen credits his team for the impressive record, especially when considering his 4.15 ERA.
"I think the reason I can get that many wins is because my teammates really picked me up during the first half of the season," Chen said through an interpreter. "Our lineup, our bullpen, my catcher, all of my teammates are playing really well."
O's: Jimenez could make rehab start Wednesday
Injured right-hander Ubaldo Jimenez will throw another bullpen session on Sunday, and if all goes well, he could make a rehab start Wednesday and potentially rejoin the Orioles when they return home from their 10-game West Coast trip on July 29.
Jimenez went on the disabled list on July 13, retroactive to July 8, with a sprained right ankle. He threw on Thursday, and manager Buck Showalter said the next hurdle for Jimenez is to pitch out of the stretch.
"Yesterday was better. The only thing he lacks is throwing from the stretch," Showalter said on Friday. "I'm hoping that goes real well Sunday and he can go out and pitch."
A's: Reddick rehabbing
The A's began the second half without outfielder Josh Reddick, who will continue his Minor League rehab assignment through the weekend.
Reddick is scheduled to play Friday, Saturday and Sunday with Class A Advanced Stockton in Inland Empire. The A's will then re-evaluate him before deciding on a return date.
Reddick was placed on the disabled list June 29 with a strained right knee for the second time in a month, at which point the A's recalled first baseman Nate Freiman from Triple-A Sacramento. Freiman could stick on the roster when Reddick is activated, since fellow first baseman Kyle Blanks (left calf) is still rehabbing.
• The O's Nelson Cruz has 28 home runs, already surpassing his 2013 season total of 27.
Mike Vernon is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.