Boston leads second-place Tampa Bay by 9 1/2 games with a magic number of four to clinch its second division title since 1995. The Yankees trail the Rays and Texas Rangers by three in the wild-card standings, with Cleveland and Baltimore also ahead of them in the race.
The Yankees had won the last two division titles and 13 of the last 17.
In his second start since coming off the disabled list, Buchholz walked four and struck out three and allowed only one unearned run.
Shortly after a pregame ceremony to honour Yankees closer Mariano Rivera in his last scheduled trip to Fenway Park, Mike Napoli hit a two-run homer off Ivan Nova (8-5) to make it 3-1 in the first inning.
TWINS 6, RAYS 4
MINNEAPOLIS (AP) — Joel Peralta gave up a solo homer to Ryan Doumit in the eighth inning and a three-run drive to Josmil Pinto, and Tampa Bay stumbled again in the AL wild-card race with a loss to Minnesota.
Tampa Bay, which had won its previous three games, wasted a 3-0 lead and dropped to 7-14 from Aug. 25 on. The Rays remained tied with Texas for the two AL wild-card spots, a half-game ahead of Cleveland.
Minnesota had lost 11 in a row to the Rays.
Tampa Bay led 4-2 in the eighth, but Peralta (2-8) blew a save for the third time in four chances. After Doumit's 13th home run of the season, Trevor Plouffe singled and Josh Willingham walked. Pinto then sent an 0-1 pitch into the Rays bullpen in centre field, the rookie's second career homer.
INDIANS 7, WHITE SOX 1
CHICAGO (AP) — Nick Swisher homered from both sides of the plate for the 13th time, Asdrubal Cabrera hit a three-run homer and Cleveland beat Chicago to pull within a half-game of Tampa Bay and Texas in the AL wild-card race.
In a game that started after a rain delay of 4 hours, 28 minutes, the Indians achieved a franchise first by sweeping a four-game series from the White Sox for the third time in a season.
Zach McAllister (8-9) allowed one run and six hits in 6 2-3 innings with five strikeouts and a walk.
Last-place Chicago has lost six in a row, and at 58-91 is 33 games under .500 for the first time since finishing 1976 with a 64-97 record, according to STATS.
Chris Sale (11-13) gave up six runs and nine hits — including three homers — in 5 2-3 innings and dropped to 6-11 following a 5-2 start. He has an 8.61
TIGERS 3, ROYALS 2
DETROIT (AP) — Alex Avila homered twice, including a tiebreaking solo shot in the eighth inning that lifted Detroit over Kansas City.
Detroit's Max Scherzer struck out 12 in seven innings, but he was denied his 20th victory when Kansas City tied it off Drew Smyly (6-0) in the eighth. Avila answered in the bottom half with a homer to right-centre.
Joaquin Benoit pitched the ninth for his 20th save in 20 chances for the AL Central-leading Tigers.
Jeremy Guthrie (14-11) pitched all eight innings for the Royals, who remained 3 1/2 games back in the AL wild-card race.
Avila's first homer was a two-run shot in the second. Alex Gordon hit a solo homer for Kansas City in the fourth.
ATHLETICS 5, RANGERS 1
ARLINGTON, Texas (AP) — Josh Donaldson, Chris Young and Josh Reddick all homered and AL West-leading Oakland completed a three-game sweep of chasing and slumping Texas.
Oakland took a commanding 6 1/2-game division lead with two weeks left after the final regular-season series between the AL West's top two teams. The A's have won five in a row and 13 of 16 overall.
Texas is 2-11 in September after beginning the month with a two-game division lead. The Rangers lost their sixth in row, all at home — this was their first winless homestand of at least six games since moving to Texas in 1972.
The Rangers and Tampa Bay are tied for the two AL wild-card spots in a rapidly tightening race. Texas starts a four-game series at Tropicana Field on Monday.
ANGELS 2, ASTROS 1
HOUSTON (AP) — Jerome Williams won a third straight start for the first time since April 2004, and Los Angeles sent Houston to its 98th loss of the season.
Houston, a big league-worst 51-98, is on the verge of becoming the first major league team to reach triple figures in losses in three consecutive seasons since Kansas City from 2004-06. The Astros were 56-106 in 2011 and dropped to 55-107 last year, their final season in the National League.
Josh Hamilton had an RBI triple in the first off Paul Clemens (4-5), a drive of the glove of centre fielder Brandon Barnes as he went up Tal's Hill. Mike Trout had reached with his AL-leading 100th walk.
Andrew Romine hit a sacrifice fly in the fifth after singles by Erick Aybar and Hank Conger.
ORIOLES 3, BLUE JAYS 1
TORONTO (AP) — Miguel Gonzalez pitched 5 1-3 innings before leaving with a strained right groin, Danny Valencia hit a two-run double and Baltimore beat Toronto.
The Orioles, who came in 3 1/2 games behind Tampa Bay and Texas in the AL wild-card race, won their first road series since taking two of three at San Francisco on Aug. 9-11.
Baltimore slugger Chris Davis, who hit his 50th home run of the season Friday, went 0 for 3 and struck out twice. He also drove in a run with a bases-loaded walk.