OAKLAND, Calif. -- The Boston Red Sox were hurting enough as it was before learning that slugger David Ortiz had a recurrence of an irregular heartbeat.
After losing to the Oakland Athletics 9-0 on Monday night, the Red Sox announced that Ortiz would leave the team Tuesday and return to Boston to be examined again for medical tests.
"He will get a clean bill of health before he plays again," manager Terry Francona said. "The games are important, but we have a responsibility to do what's right."
Big Papi was a late scratch for what was first thought to be the flu. Ortiz, who on Sunday hit his major league-leading 47th home run at Seattle, already spent time in a Boston hospital earlier this month for the condition. He said he thought it was caused by fatigue.
Ortiz was scheduled to be seen by Dr. Larry Roman.
"It's not good," Boston reliever Mike Timlin said. "This game is nothing compared to someone's health or family. We don't play games with people's lives. I don't know any of the details. All I can do is pray for him."
Francona, general manager Theo Epstein and trainer Paul Lessard met with Ortiz just more than an hour before game time.
"We honestly think he's OK, but he can't play like that," Francona said. "We can't do it."
Frank Thomas hit his 476th home run, Nick Swisher connected three batters later and Esteban Loaiza completed a perfect August by winning his fourth straight decision for the AL West-leading A's.
Pinch-hitter Adam Melhuse hit a two-run homer in the eighth, and Bobby Kielty and Jay Payton each drove in two runs for the AL West-leading A's, who increased their division lead to 6½ games over Los Angeles after the Angels lost 2-0 at Seattle.
Thomas hit his 28th homer of the year leading off the seventh against Keith Foulke, moving past Willie Stargell and Stan Musial for 23rd on the career list. Swisher also has 28 home runs, tied with Thomas for the team lead.
"It's been a great comeback year," said the 38-year-old Thomas, plagued by injuries the past two seasons with the Chicago White Sox. "It's great to be helping the team, especially in the stretch drive when it counts."
Melhuse hit his fourth home run of the year, the first pinch-hit homer by an A's player since Scott Hatteberg at Seattle on July 21, 2004.
Loaiza (8-7) went 4-0 in August for a season-best winning streak, equaling his best stretch from 2005. Kielty and Payton each hit RBI doubles in the third and Thomas also drew a bases-loaded walk on a cool Bay Area night when the first-pitch temperature was 60 degrees.
Kielty had a fourth-inning RBI single and Payton added a sacrifice fly in the inning.
The Red Sox had just six hits in losing their fourth straight and 10th in 12, falling seven games behind the idle first-place New York Yankees. Boston's AL East deficit is its largest since it was down 7½ games on Aug. 20, 2004.
Boston is 8-19 in August, losing 19 games in a month for the first time since April 1996. This marks Boston's first August with more than 18 losses since dropping 21 in August 1985.
Kason Gabbard (0-3) didn't allow a hit until Kielty's one-out RBI double in the third. He was done an inning later after allowing four straight singles, including Kielty's RBI single. Bryan Corey relieved and issued Thomas' third free pass of the game, bringing in a run.
Loaiza, who pitched a four-hit shutout last Wednesday at Toronto, threw seven shutout innings. He allowed five hits, struck out four and walked one. He hasn't given up an earned run in three starts since Aug. 13, 22 2/3 innings.
Boston, swept at Seattle last weekend, was without the heart of its batting order. Along with Ortiz, left fielder Manny Ramirez missed his fourth start in five with a sore right knee and wasn't expected to play all series.
The team also sent pitcher Kyle Snyder back to its hotel because of the bug that has been going around the clubhouse.
Carlos Pena made his Boston debut and started at first base after the Red Sox purchased his contract from Triple-A Pawtucket earlier in the day. On one play, he dived over the short padded wall along the first-base line and fell awkwardly into the crowd before getting up unharmed.
The grounds crew added dirt to the mound in the bottom of the first after Gabbard gave up a leadoff walk to Jason Kendall and apparently was dissatisfied with the condition of the mound, which drew boos from the crowd. Then, the crew came out again to rake the mound before the top of the second.
Neither team took batting practice as the grounds crew worked to finish the transformation of the field, which was used by the NFL's Oakland Raiders for an exhibition game Friday night and a fan rally Sunday.
- Oakland is a majors-best 30-13 since the All-Star break and 19-6 in August
- The A's have not lost in nine series -- winning all those except for a four-game split last week at Kansas City -- since Boston took two of three from Oakland July 24-26.