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9/8/2013 4:48 P.M. ET

Donaldson given day off to rest ailing quad

OAKLAND -- Josh Donaldson arrived at O.co Coliseum on Sunday morning expecting to play in the series finale with the Astros, but he was given the day off after tweaking his strained right quad during Saturday's game.

"Sometimes I just ask the trainer," A's manager Bob Melvin said. "The trainer believes this is what we should do, and I agree."

Sunday was just the third time in 141 games this season that Donaldson was not in the starting lineup. Melvin said Donaldson could be used as a pinch-hitter but preferred to keep him fresh for Tuesday's series opener at Minnesota.

"He's a true grinder," Melvin said. "He can play with some nicks, some aches and pains, but this is one where we just felt like it was prudent to leave him out today."

"I never want to miss a game," said Donaldson, one of the A's most fiery competitors. "But I think it's best right now."

Alberto Callaspo made the start at third base, with Eric Sogard batting second in the lineup and playing second base. Donaldson is batting .362 with eight runs, eight doubles, one triple, two home runs, seven RBIs and six multihit games over his past 12 contents, all of which came with him batting second in the order.

"It makes it easier having a true third baseman like Callaspo, but it's always tough to give [Donaldson] a day off because he does want to play every day," Melvin said. "This time of year, every game is really important, and he's an important part of our lineup, so it's difficult to have him out. But with the off-day [Monday], it is definitely the prudent thing to do."

A's bullpen coming together for stretch run

OAKLAND -- The A's bullpen has allowed just six runs over the past nine games after allowing 28 runs over its previous 10.

A staple of the team's success this season, the relievers are primed to play a pivotal role in the A's postseason push after doing so in last season's September stretch to overtake the Rangers.

"We're trying to keep some guys available every day," A's manager Bob Melvin said. "You try to resist the temptation of using the same guys every day, and we've also had guys who've stepped up, like Dan Otero."

Sean Doolittle earned his first save of the season in Saturday's 2-1 win over the Astros and said he felt the added pressure of pitching in the ninth inning in place of closer Grant Balfour, who received the day off after a 35-pitch outing Friday.

Doolittle and Ryan Cook, who served as Oakland's closer for a stretch last season, are viable options when Balfour is unavailable. Melvin said he'd prefer not to use Balfour on Sunday in order to give him three days' rest with Monday's off-day.

"We're probably a bit deeper, but you do understand that this time of year these guys have a lot of heavy workloads and you just have to find that extra gear down the stretch," Melvin said.

Even Opening Day starter Brett Anderson has two saves for the A's since his recent return from a fractured right foot. And that stat isn't lost on Doolittle.

"It feels good," Doolittle said, "because Brett has two, and now I'm almost going to catch him. He's been in the bullpen like a week."

Worth noting

• Right-handed reliever Dan Otero will leave the team following Sunday's game against the Astros to join his wife for the birth of their child. He will join rejoin the A's on Wednesday in Minnesota, said A's manager Bob Melvin.

• Houston scratched starter Paul Clemens from Sunday's game because of a blister, and Lucas Harrell made the spot start. Both are right-handed pitchers, so it didn't affect Melvin's matchup-based lineup.

Jeff Kirshman is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.