"It's great," A's manager Bob Melvin said of Semien's return. "You look at our lineup and it looks like it has a little more length. Some more oomph in it. It's good to get him back. Obviously we've missed him at some point. We've seen some other guys, whether it's Pinder or Barreto, guys we know that will be a big part of our future. It's good to see those guys, but it's always good to get your shortstop back."
In Thursday's 7-4 win over the Mariners, Semien went 1-for-4 with a walk and two strikeouts.
Semien, 26, played in eight rehab games, three with Class A Advanced Stockton and five with Tripe-A Nashville to complete his recovery process.
"It felt great," Semien said. "When I got to Nashville I started to feel a lot better and pain-free. I'm able to fire my hands the way I used to, which is good. It took a while. It took almost 80 days since surgery. But I'm glad I'm back."
Cotton left the Athletics' June 23 contest with the White Sox because of a blister on his right thumb, and he had his subsequent start pushed back because of it. This time, it's the callous next to the blister that's causing him problems, according to Melvin.
Melvin said he doesn't anticipate Cotton to be out long, but he also has some reservations.
"We are planning on him being ready to pitch early within the first five days of the second half, and that's the reason we put him on the DL here," Melvin said. "But who knows how these things go. We thought we were out of the woods with him last time, but it was the next day the callous got split open."
The rookie righty has a 5.17 ERA in 14 starts this season.
Right-hander and long-time Minor Leaguer Chris Smith, 36, will make his first Major League start in place of Cotton on Saturday, facing Seattle rookie right-hander Andrew Moore. He made 13 relief appearances for the A's last season and owned a 2.92 ERA in his first MLB season.
"We're excited about that," Melvin said. "That guy made a big impression on us last year. As a teammate, what he's been through, has a smile on his face whether he's in [Class A] or in the big leagues. Got some time and was effective for us last year, and to be able to get a start. I know he'll be really excited about that. As are we."
• Starting pitcher Andrew Triggs was transferred to the 60-day disabled list with a strained left hip. He was 5-6 with a 4.27 ERA in 14 starts this season. … Right-handed pitcher Ryan Dull (strained right knee) is throwing live batting practice Saturday in Arizona … Right-handed pitcher Kendall Graveman (right shoulder strain) is throwing a 40-pitch bullpen session on Thursday in Arizona … Infielder Chad Pinder (strained left hamstring) hit in the cage and is running "much better," according to Melvin … Right-handed pitcher Bobby Wahl (strained right shoulder) to throw a 15-pitch flat-ground session on July 20. … Right-handed pitcher Chris Bassitt (Tommy John surgery) will throw one inning (25 pitches) in Advanced-A Stockton on July 20.
Josh Horton is a reporter for MLB.com based in Seattle. He covered the A's on Thursday.