NEW YORK -- In what has become something of a trend, the Yankees suffered two familiar losses Friday night.

One was a player to injury; in this case, it was CC Sabathia, who left the game after three innings with another right knee issue. The other was a game to the Athletics, opening the three-game series at Yankee Stadium with an 8-2 loss to Oakland, their fourth in four meetings this season.

• Box score

Although October has typically been a different story -- New York has eliminated Oakland from the postseason three times since 2000, most recently in last year's American League Wild Card Game -- this latest trend has to be concerning to a Yankees team with championship aspirations.

"We're a confident group, whoever we play," manager Aaron Boone said. "Obviously, Oakland beat us up a little bit out there and got us here, but as far as how that affects us moving forward and who we'll see, I don't worry about that at all."

Sabathia allowed one run over the first three innings, the lone Oakland hit against him coming on Jurickson Profar's second-inning home run. But Sabathia left the game prior to the fourth as his troublesome right knee -- one that has already landed the lefty on the injured list twice this season -- apparently flared up with what the Yankees termed "discomfort."

"I could tell early on tonight that he was struggling with it," Boone said. "The warrior that he is, he pitches as effectively as he did."

Didi Gregorius' RBI fielder's choice tied the game in the third inning, while Mike Tauchman's bases-loaded double play -- which came after Boone challenged a double play, getting both outs correctly overturned to set up a bases-loaded, no-out opportunity -- gave them a 2-1 lead.

Luis Cessa threw a pair of scoreless innings in relief of Sabathia, but Tommy Kahnle had his worst outing since early June, allowing three runs in the sixth after giving up just four runs total over the past two months. Profar's two-run double highlighted the frame for Oakland, which added two more runs in both the seventh and ninth innings to extend a lead it would never relinquish.

"We pretty much haven't seen that outing," Boone said of Kahnle. "The occasional time he has even gotten dinged, they may have run into a homer off of him or something, but for them to string a little rally against him ... I don't think he had his fastball command. It wasn't much of a factor for him tonight. Overall just not very sharp, which he's been as much as anyone on our club. He's been so efficient and so sharp time after time, but tonight was just an off one for him."

Left-hander Brett Anderson limited the Yankees' offense to two runs over six innings, giving up six hits and two walks, striking out one. Yusmeiro Petit followed with two perfect innings, then Blake Treinen retired the side in order in the ninth to finish up the win. The Yankees didn't have a hit after the fourth inning as Oakland retired the final 16 New York hitters.

"Certainly it's going to happen from time to time where you go through a stretch where they're going to hold you down for a handful of innings, whatever it might be," Boone said. "It is a little bit unusual, because I always expect our guys to do some damage at some point. Credit to them; they were able to run through us there, and after they were able to rally in those middle innings, their pitchers really held it down."