"He's throwing extremely well," Geren said at the time of Marshall's promotion. "It should be nice for Breslow to have another lefty down there."
Marshall, who pitched in 51 games for the A's in 2007 after being selected from the White Sox organization in the Rule 5 Draft, posted a 1-2 record and a 6.43 ERA but did not pitch in the Majors last season.
Since rejoining the big boys in Oakland, Marshall has been given four innings of work, giving up four runs -- all against the Yankees on Tuesday -- while walking none and fanning one.
Although the 26-year-old has much to prove, he's already got the support of his manager.
"He's older and more mature," Geren said. "This time around he seems to look more comfortable. Before, everything was probably a little more accelerated.
"He's had time to digest the experience, which makes him better."
Marshall recorded seven saves and a 3.20 ERA in 50 appearances with the River Cats, and his return to the Bay comes after lowering his release point at the beginning of the season.
"It kind of makes him similar to Ziegler," said Geren, referring to sidearmer Brad Ziegler. "Basically, it just gives us another arm out of the bullpen, which is nice."
Marshall, who recorded an out in Friday's 3-2 loss to visiting Detroit, has a decent shot at seeing action in the finale of the three-game set on Sunday due to the heavy left-handed-hitting nature of the Tigers' lineup.
OAK: RHP Brett Tomko (2-2, 4.21 ERA)
The A's signed Tomko to a Minor League contract on Aug. 5. On Monday, he was back in the Majors, facing the same Yankees team that released him earlier this season. The 36-year-old held New York to five hits over five innings, leading the A's to a 3-0 win. "It's been a long road this year," Tomko said. "It was kind of ironic that my first start here came against the Yankees." He'll look to keep things going against the Tigers. He hasn't faced them this season.
DET: RHP Rick Porcello (10-7, 4.21 ERA)
Porcello's first outing after his five-game suspension for throwing at Boston's Kevin Youkilis should provide a better idea whether he's on his way to a high-strikeout finish. He used the combination of a devastating offspeed pitch and his usual biting sinker to rack up eight strikeouts over 5 2/3 innings against the Mariners on Tuesday at Comerica Park, but he left with trouble on the bases with two outs in the sixth and 93 pitches thrown. The hope for the Tigers now is that they won't have to watch his innings quite so closely with the time off he got from the suspension and the second-inning ejection that led to it.
Geren said there is no timetable for the return of Dallas Braden (left foot infection) to the mound. "He's not getting better as quickly as we hoped," the skipper said. "He's a couple weeks away from the mound." The lefty has not thrown in a couple of days and is scheduled to stay off his feet for awhile to help calm his foot's nerves. ... Leadoff hitter Adam Kennedy grabbed three hits in Saturday's game after going 8-for-36 in his previous eight games. "It's hard to put a finger on it," Geren said of the third baseman's recent struggles at the plate. "He's battling up there, going through ups and downs. When you get in a right situation, you still want him up there." ... Gio Gonzalez's father, Max, spent time on the field with his son and met several of the lefty pitcher's teammates during batting practice on Saturday.
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Official game notes
KTRB 860, KDYA 1190 (Español)
Monday: Athletics (Vin Mazzaro, 4-8, 5.31) at Mariners (Ian Snell, 3-9, 5.60), 7:10 p.m. PT
Tuesday: Athletics (Brett Anderson, 7-9, 4.51) at Mariners (Ryan Rowland-Smith, 2-1, 4.24), 7:10 p.m. PT
Wednesday: Athletics (Gio Gonzalez, 4-4, 5.78) at Mariners (Lucas French, 3-3, 3.83), 7:10 p.m. PT