OAKLAND -- A constantly rotating A's infield mix added Adam Rosales on Thursday, when Brandon Hicks was optioned to Triple-A Sacramento after struggling to provide offensive consistency in 20 games with Oakland.

Hicks hit just .183, but his presence was felt by way of a handful of game-changing hits -- including his game-tying home run against the Rays on Monday that paved the way for a 15-inning A's victory. He belted three homers with the A's and compiled seven RBIs, while playing mostly against left-handers.

"When I talked to him earlier today," manager Bob Melvin said, "I said, 'Everybody felt the effects when you were here. Your numbers are in no way indicative of what you've meant to this team.' He probably single-handedly won two games for us, and every hit that he had had a big impact. He was sub-.200, but every hit was big for us, he was a good fit here, and I'd be surprised if we don't see him again at some point this year."

In the meantime, Rosales is the latest to get a shot at helping an infield depleted of regular shortstop Cliff Pennington, who will begin a rehab assignment at Triple-A on Friday as he continues to recover from left elbow tendinitis.

This marks Rosales' third stint with the A's this year, having compiled a .167 average with three RBIs in his previous 13 games with the club. With Sacramento, he posted a .280 average to go along with eight home runs and 47 RBIs in 76 games, making most of his appearances at shortstop while also seeing time at second and third base.

"One of the things we've done well, certainly in the last month, is get guys here when they're playing well, get them in the lineup and take advantage of that production," Melvin said. "We're just trying to get guys here and get more protection at a time when they're playing well."

Rosales was inserted into the lineup Thursday, batting eighth and starting at shortstop for the club's four-game-series opener against Toronto.

A's await MRI on Smith's strained hamstring

OAKLAND -- A's outfielder Seth Smith, serving as designated hitter on Thursday, left Oakland's 4-1 victory over the Blue Jays after sustaining a strained left hamstring while running out a groundout in the fifth inning at the Coliseum.

Smith, who put the A's on the scoreboard with an RBI single in the third inning to snap an 0-for-18 skid, was replaced in the seventh by Chris Carter.

The extent of his injury is not yet known, but the A's should have a better idea after he undergoes an MRI exam on Friday.

"I iced it, and it's still stiff, still sore, so I'll get an MRI tomorrow and see where to go from there," Smith said. "It's one of those things, you really can't speculate on until you wake up the next day and see where it is then."

It's the first injury of the year for Smith. If he were to be placed on the disabled list, the A's have a handful of outfielders at Triple-A whom they could look to for help, including Michael Taylor and Collin Cowgill.

Blackley returns to bullpen

OAKLAND -- Leave it to Travis Blackley to find a positive in being moved back to the bullpen.

"I get to pitch more often anyway now," he said, smiling.

The A's left-hander, who began his stint with the club in the bullpen, has returned to the familiar role to accommodate the addition of righty Dan Straily, who is slated to make his much-anticipated big league debut on Friday.

Blackley will serve in a long-relief role for an already stacked bullpen that entered the day with an American League-best 2.82 ERA. This coming on the heels of a stellar stretch as a starter, with Blackley going 3-3 with a 3.62 ERA and 38 strikeouts next to just 15 walks in 59 2/3 innings spanning 10 starts.

"To fit somebody in, you sometimes have to do something that's a bit uncomfortable, and with everybody pitching well, somebody has to wear it and go to the bullpen, and Travis was great about it," manager Bob Melvin said. "We have a lot of faith in what he's doing for us now."

"I just enjoy being a part of this team," Blackley said. "You look at this clubhouse, you see it -- it's just a good environment to be in. If it means I have to go to the 'pen, there's no worries, man. I love pitching, no matter where it is.

"[Melvin] said I had done everything they asked and more and were very happy with what I've done, that this didn't reflect the way I'd been pitching."

Blackley finds comfort in knowing he'll likely now only have to face a team one time through the order, which allows him to immediately show each of his four pitches and let his fastball go, making his offspeed repertoire that much better.

In turn, he recognizes the talent Straily lends to the organization.

"It doesn't seem like there's been a level yet that he hasn't been able to hold down," Blackley said. "Obviously this is the big leagues, a little bit different, but by the sounds of how things have gone down there, this shouldn't be too much of an issue."

Worth noting

• Outfielder Coco Crisp returned to the lineup Thursday after missing four straight games with left hamstring tightness. The A's went 1-3 without Crisp, who entered the day batting .366 over his previous 10 games.

"It's always nice to get Coco back in the top of the lineup," Melvin said. "He does a lot of good things for us, whether it's defensively in center, whether it's getting on base and creating havoc on the bases, or he's been known to come up with some really big hits for us. We feel the effect of having him in the lineup."