The Houston Astros, the three-time defending American League West champions, appear as vulnerable as any point since 2016, the last time Houston failed to qualify for the postseason.

The Astros' losing streak hit five games on Sunday at Oakland, falling to the Athletics 7-2 to complete a 3-6 roadtrip and not only fall 5 1/2 games behind Oakland, but also a half-game behind the second-place Texas Rangers.

The Astros return home to host the San Francisco Giants on Monday for a three-game interleague series with their pitching staff in tatters and the aura of invincibility they've carried for three seasons nowhere to be found.

"It's definitely down a little bit," Astros catcher Dustin Garneau said of the clubhouse mood. "(The road trip) was tough. We're going to go home and start something new and get back in the swing of things."

How the Astros manage a bounce back at this stage remains to be seen. They are without their ace (Justin Verlander) plus their closer (Roberto Osuna), and an avalanche of injuries have forced manager Dusty Baker to rely upon rookies in his bullpen. Houston appeared capable of slugging its way past opponents before the Athletics limited the Astros to five runs in the series.

The series finale featured a seventh-inning, dugout-clearing scuffle sparked by a heated conversation between Oakland center fielder Ramon Laureano and Astros hitting coach Alex Cintron. The incident was the latest blight on an Astros season thus far bloated by distress.

"No, it's a long way from spiraling out of control," said Baker, who was ejected in the top of the seventh for arguing balls and strikes. "We're not playing good baseball, and we ran against a team that is hot. We've got to go home and regroup and start all over again."

Said Astros outfielder Josh Reddick: "Definitely a tough spot for us right now. We haven't hit our stride yet this year.

"We're just not getting the job done, and that's unacceptable on our part."

The Astros on Sunday acquired left-hander Brooks Raley from the Cincinnati Reds for a player to be named later. Raley will report to Houston after being added to the major league roster.

Right-hander Lance McCullers Jr. (1-1, 9.22 ERA) will start the series opener for the Astros. McCullers has struggled in his return after missing the 2019 season following Tommy John surgery, particularly over his previous two starts against the Los Angeles Angels and Arizona Diamondbacks.

He allowed 12 earned runs on 12 hits and four walks with just five strikeouts over 7 2/3 innings in those two games. Opposing batters also slugged .750 against McCullers in those starts.

McCullers will make his first career appearance against the Giants and his ninth interleague start. He is 2-2 with a 4.04 ERA against the National League with 43 strikeouts in 42 1/3 innings.

The Giants dropped the rubber match of their weekend series with the Los Angeles Dodgers 6-2 on Sunday. Right-hander Kevin Gausman produced the first quality start of the season for San Francisco, carrying a shutout into the seventh inning, only for the bullpen to undermine his effort.

The Giants did not announce a starter for Monday but rookie right-hander Logan Webb (1-0, 2.13 ERA) is due to take his turn in the rotation. Webb earned his first win of the season in his previous start against the Colorado Rockies on Aug. 5, allowing two runs (one earned) on four hits with four strikeouts over five innings in a 4-3 victory.