SEATTLE -- Yoenis Cespedes' return to the A's outfield was short-lived, as the Cuban slugger exited Friday's 8-2 victory over the Mariners in the fourth inning with shoulder stiffness.
Cespedes didn't play in Saturday's game, and Oakland manager Bob Melvin said that the outfielder is day to day.
"I won't know until we figure out how severe it is, so, I mean, he does have a dramatic swing, there's a lot going on," Melvin said. "He creates a lot of torque, that's just who he is, but there is a concern that he's had a few days off, then we got him back in the field and had to take him out. But hopefully it's something that's manageable here pretty soon."
Without Cespedes, the A's are missing one of their hottest players. Cespedes is batting .314 in September, and he is second in the American League with 19 RBIs in the month and tied for third with six home runs.
Norris keeps showing pinch-hitting power
SEATTLE -- Derek Norris hit his third pinch-hit home run of the season in Friday's 8-2 win over the Mariners, making him the first A's player to do so since 1982, and just the fifth in club history. All three of Norris' hits as a pinch-hitter have gone deep, driving in five runs for Oakland. Although he is only batting .200 as an offensive substitute, he has an OPS of 1.094.
Manager Bob Melvin credits Norris' success to the slugger's focus and preparation, as well as the tendency to use a pinch-hitter in aggressive situations with favorable pitching matchups.
"He knows when the situation potentially comes up and a lot of that really combats the [obstacle of] not being in the game," Melvin said. "Pinch-hitting can be a hard thing to do sometimes, but if you know ahead of time, you're prepared for it mentally and then you go in the cage, take some swings and you're even more prepared when you go out there."
Norris admits that while it's nice to have had some success in the role, he's a long way from becoming a master of pinch-hitting.
"I've had some success and I'll credit some success to the fact that I've just gotten some decent pitches to get and I haven't missed them," Norris said. "But as far as, 'I've figured out this whole pinch-hitting thing,' never.
"Because this is the hardest thing to do in all of sports is hit a baseball, and to hit a baseball out of the ballpark is very, very tough to do. If you think about hitting a round ball and a round bat squarely, it doesn't make a lot of sense."
Cook regains form, fixes command issues
SEATTLE -- A's fans can rest easy know that Ryan Cook is on the rebound. Cook was an essential part of Oakland's bullpen for much of the year, but he has struggled in September, seeing his ERA balloon from 2.12 to 2.69 -- its highest mark since April 6.
But in his last two appearances, the 24-year-old righty has pitched well, giving up just one hit while striking out two over 1 2/3 innings. While the young reliever didn't make any significant mechanical adjustments, he's fixed the command issues that plagued him earlier in the month.
"Sometimes it's just something mentally to get you going in the right direction, the times that you do get out of whack and you have to make some adjustments," manager Bob Melvin said. "Sometimes it's just as big for you mentally as it is physically, and it's all about him throwing the ball over the plate. When he throws the ball over the plate it's really good, so we've seen that the last couple times out."
With the playoffs just around the corner, Cook's resurgence couldn't have come a moment too soon. Still, the 2012 All-Star said he didn't feel a sense of urgency to regain his old form with the postseason fast approaching.
"I feel like I know who I am as a pitcher and it was just about getting back to that and keeping that mentality," Cook said.
• Melvin said that while many of his players -- particularly in the bullpen -- are ready for a break, he's concerned about them having too much time off between Sunday's regular-season finale and the A's first game of the playoffs on October 4.
"I think there's some aspects you like with the break and some that you don't," Melvin said. "You kind of want to stay current and we'll combat that with some situational stuff."
• The A's have lost the season series with Seattle, meaning they'll continue a streak of winning in even numbered seasons and losing in odd numbered seasons over the past eight years.
Jacob Thorpe is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.