OAKLAND -- The Boston Red Sox are in freefall mode down the stretch for the second consecutive year.
The Oakland A's, meanwhile, are surging toward the playoffs.
Two teams heading in different directions opened a series Friday night at the Coliseum, and the A's obliterated the Red Sox 20-2.
George Kottaras had career highs with two home runs and five RBI in Oakland's highest-scoring game in nearly 12 years.
Josh Reddick, like Kottaras, a former Boston player, tortured his old team by hitting his first career grand slam to highlight the nine-run seventh inning.
Brandon Moss went 4-for-4, hit a two-run homer and had a pair of run-scoring doubles. Josh Donaldson hit a two-run homer, and Jonny Gomes had two RBI singles during the Athletics' seventh straight win. The A's have a one-game lead over the Baltimore Orioles for the first of two American League wild-card playoff positions.
The Red Sox, coming of a sweep at the hands of the Los Angeles Angels, have lost the first four games of their West Coast road trip.
Oakland's Brandon McCarthy pitched 6 1/3 innings and allowed eight hits and two runs to earn his first home win since June 19. McCarthy (8-5) has tossed at least six innings in 14 of his 17 starts this season.
The 20 runs were a season high allowed by the Red Sox.
Boston starter Aaron Cook, a sinkerball pitcher, did not have the usual downward movement on his pitches. He was lit up for six runs on seven hits in 2 2/3 innings, recording only two groundouts.
The A's surged in front with a four-run rally in the second inning. Moss' double drove in Yoenis Cespedes for the first run. Moss scored on a Gomes single. Donaldson followed with a two-run homer to cap the inning.
The third inning included some deja vu from the second, as Moss hit an RBI double and was singled home by Gomes. The latter hit drove Cook from the game.
The second Boston reliever was Alfredo Aceves, the recently deposed closer. He gave up a two-run homer to to Moss in the fifth, pushing Oakland's advantage to 8-1.
Oakland expanded its margin to 18-2 in the seventh, scoring four runs.
Kottaras, who homered in the sixth inning, hit a two-run single. Cliff Pennington also doubled in a run. Reddick homered to right field, his 28th homer of the season and his first career grand slam.
After Adam Rosales doubled to right in the eighth inning, Kottaras made it an even 20 runs by hitting a line-drive home run to right field.
Red Sox catcher Jarrod Saltalamacchia homered in the fourth inning, his 23rd of the season.
NOTES: Red Sox second baseman Dustin Pedroia has an 11-game hitting streak. He has 995 career hits. ... Boston is a season-worst nine games under .500. ... Red Sox reliever Daniel Bard made his first appearance since June 3. He allowed one run in one inning. ... Moss had his first career four-hit game. ... Oakland has tied its season high with seven consecutive victories. ... The Athletics have hit four or more home runs in a game on consecutive days. ... The A's recalled left-handed reliever Pedro Figueroa from Triple-A Sacramento for his fifth big-league stint of the year. Oakland demoted right-handed reliever Jim Miller to Class A Stockton, and he will return next week after the California League season ends. The A's didn't send Miller to Sacramento because the River Cats are headed for the Pacific Coast League playoffs.