Kottaras homered for the second straight game and Anderson won his fourth straight start since recovering from Tommy John surgery as they helped the A's beat the Seattle Mariners 6-1 Saturday night.
Anderson (4-0), who had surgery on his left elbow 14 months ago, allowed one unearned run and six hits while striking out four in six innings. He lowered his ERA to 0.69. He has 19 strikeouts in his four starts.
"I think it's been more than we could ever expect," A's manager Bob Melvin said of Anderson's recovery. "To sit here and say he's 4-0 at this point coming off that is pretty terrific."
Kottaras, acquired July 29 in a trade with Milwaukee, has had an offensive revival with the A's. He has had 16 RBI in his 13 games with Oakland -- 13 in the last five games. With the Brewers, he drove in just 12 runs in 58 games.
With the score tied 1-1, Yoenis Cespedes opened Oakland's fourth with a double into the left-field corner. With one out, he stole third on a 1-0 pitch to Stephen Drew, who followed with a RBI single against the drawn-in infield. The ball just tipped off the glove of second baseman Dustin Ackley.
Kottaras then hit a 1-1 slider from Hisashi Iwakuma (6-4) for a two-run, line shot into the right-field seats to make it 4-1. It was his fifth home run of the season, and came one day after he had a three-run shot in the same inning Friday during the A's 6-1 victory. It was the first time he hit a home run in back-to-back games.
"He's been pretty amazing," Melvin said. "You look at his average (.222) then you look at his home run numbers and RBIs. It seems like every home run he has hit for us has been a big home run. And tonight's home run really had the same affect as last night's home run."
Both home runs gave the needed room for the A's starters to work. He hit his three-run home run Friday off Felix Hernandez. He hit his two-run shot off Iwakuma, who was 5-1 with a 1.57 ERA in his last seven starts. He was 3-1 with a 2.05 ERA in five August starts.
"Iwakuma has been pitching lights out," Melvin said. "He's been giving up two runs or less just about every game so he's been on a roll. For us to score some runs early again off of him was pretty impressive as it was off Felix."
Iwakuma, who worked 3 2/3 innings, allowing four earned runs and six hits, said through an interpreter that the slider Kottaras hit "was kind of a cookie, kind of easy to get a home run. I need to concentrate on that pitch."
Coco Crisp had a run-scoring double after Kottaras' homer that gave Oakland a 5-1 lead.
The A's kept pace in the AL West with the Texas Rangers, who beat Tampa Bay 4-2. Oakland trails the Rangers by 4 1/2 games and are in a virtual tie with the Yankees and Orioles atop the wild-card race.
"Oh, he looked pretty good to me," Mariners manager Eric Wedge said of Anderson's effort. "He did a good job with his fastball. He has a lot of confidence with that breaking ball he throws. He controlled the tempo of the game."
Seattle finished 0 for 7 with runners in scoring position.
"I always hold myself to a high standard. You have to in this game, otherwise the game's going to beat you up," Anderson said. "Today was my most grinding start so far. It seemed like it was first and second one out every inning.
Anderson and Kottaras have had significant roles in helping the A's win 17 of their last 22 games. Their 78 wins are also four more than all of last season.
"Definitely getting more frequent at-bats helps," Kottaras said. "I just taking advantage of mistakes that are tossed up there.
"I think I've gelled pretty good with the guys and doing what I can to help and have a good time."
The A's forced Iwakuma to throw 25 pitches in the first inning and scored a run without a hit.
Crisp opened with an eight-pitch walk. He was forced at second on Josh Reddick's grounder. Cespedes followed with a two-out, one-hopper past third baseman Kyle Seager and into the left-field corner. It was ruled a two-base error, scoring Reddick.
The Mariners tied it in the second. Michael Saunders bounced a one-out double over the center-field wall. Miguel Olivo reached when shortstop Drew booted his ground ball, advancing Saunders to third. He then scored on Trayvon Robinson's force-out.
Cespedes added a sacrifice fly in the ninth.
A's RHP Brandon McCarthy, hit in the head by a line drive Wednesday, is showing good progress after his surgery to reduce brain swelling. "I'd give him one more day (until he's out of the woods)," trainer Nick Paparesta said. "I think with any head injury you need to be cautious ... but the progress has been great and we're all very excited about it." A's manager Bob Melvin, who gathered the team together before the game for a medical update, said, "It puts a smile on your face." ... Reddick's single in the ninth snapped an 0-for-18 slump. ... Wedge said rookie RHP Erasmo Ramirez, a September callup, will start Tuesday at Toronto. Hector Noesi also will be worked into the rotation. "We just want to take a look at them again," Wedge said. "It's a chance to watch them a little longer." ... Mariners LH reliever Oliver Perez has not allowed a run in his last 18 appearances (13.1 innings), or since July 8. That's tied for the seventh-longest streak in club history.