Terry Francona earned his 1,000th win as a major league manager, the 57th to reach that milestone, and the eighth still active. Boston moved a season-high three games ahead of the New York Yankees for the lead in the AL East.
Meanwhile, the Mariners tied the 1992 team's mark after loading the bases in the eighth against Daniel Bard, but the reliever got out of the jam. He has now held teams scoreless in 24 straight innings over 23 outings, the longest active shutout streak in the majors.
Beckett (9-3) allowed seven hits and one walk and struck out seven. The only run he allowed came on a homer in the seventh by Mike Carp, his second in two nights since being recalled from Triple-A Tacoma last Monday.
Blake Beavan (1-2) retired the first two batters in the bottom of the seventh then allowed three straight hits, including the single by Ellsbury, who scored on a wild pitch by reliever Aaron Laffey.
Jonathan Papelbon pitched the ninth for his 23rd save in 24 chances.
Dustin Ackley began the eighth with a single and took second on a walk to Justin Smoak. Adam Kennedy then bunted, and Bard fielded it and threw to third baseman Kevin Youkilis, whose foot was off the base. Then Bard retired Carp on a shallow fly to left, Jack Cust on a strikeout and Franklin Gutierrez on a groundout.
Both teams had five hits through six innings. The Mariners had left four runners in scoring position through six innings before Carp's homer.
Cust was stranded at second after a two-out double in the second. Smoak also was left at second in the fourth after grounding into a forceout and advancing on a wild pitch by Beckett. And Seattle stranded runners at second and third in the sixth after the first two batters, Ichiro Suzuki and Brendan Ryan, singled.
The Red Sox got a one-out double in the first from Dustin Pedroia, but the next two batters struck out. The hit extended Pedroia's career-best hitting streak to 20 games.
Boston nearly scored in the second when David Ortiz led off with a double and took third on a single by Carl Crawford. Josh Reddick popped out to second base before Jason Varitek hit a flyball to medium center field. Gutierrez made the catch, then threw home on a fly to double up Ortiz, who had tagged.
The Red Sox got another runner to third in the third. Ellsbury started the inning with a single and kept going to second when the ball got by left fielder Carp for his second error in two days. Ellsbury took third on a groundout, but was stranded when Adrian Gonzalez flied out.
Gonzalez got a one-out double in the sixth, but was tagged out when Youkilis grounded to third.
Notes
Pedroia has reached base in 32 consecutive games, the longest active streak in the majors… Carp had been optioned to Triple-A Tacoma on July 3 when Beavan was called up. … Former Red Sox third baseman Mike Lowell, who retired after last season, threw out the ceremonial first pitch. … Beckett has allowed more than three runs just twice in his 19 starts this season. … Beavan has allowed a total of nine runs in his four starts.