BOSTON -- In some respects, stability has been hard to come by for Jacoby Ellsbury this season. His spot in the batting order seems to change by the week, hardly allowing the Red Sox center fielder an opportunity to expect where he'll be slotted each day.

But for all the unpredictability surrounding the lineup placement of Boston's sparkplug, one facet of his game has remained lethal regardless of where he hits -- speed.

"He's one of the elite basestealers in the league," said manager Terry Francona, whose Red Sox will close out a three-game series against the Mariners on Sunday at Fenway Park. "The same problems we have with a guy like Carl Crawford in Tampa Bay, other teams have to deal with against us."

With a stolen base in the second inning of Saturday's 3-2 loss to the Mariners, Ellsbury etched his name into the franchise record books. The 25-year-old has now swiped 35 bases in each of his first two full Major League seasons, and he's the first Red Sox player to record 35 steals in back-to-back years since Hall of Famer Tris Speaker (1912-14).

Saturday's theft also vaulted Ellsbury past Otis Nixon for the second-highest pre-All-Star break total by a member of the Sox since 1954. Boston's 2005 first-round Draft pick is the first American Leaguer with 35 or more stolen bases before the break in consecutive seasons since Rickey Henderson (1988-90).

Following Saturday's game, Ellsbury trails only Crawford's 40 steals for the Major League lead. Coming off a rookie year in which he stole 50 bags, four shy of Tommy Harper's club record of 54, Ellsbury is primed to set the team's single-season record in 2009.

"Hopefully, I'll look at the end of the season and say, 'Hey, I did everything I could,' and the numbers will speak for themselves," Ellsbury said. "That's kind of how I go about it. Obviously, I want to be probably right around that 50 range, but that's not a mark I set for myself, like, 'Hey, I need to get 50.'

"Last year, if I had said, 'I want to get 40,' I might have slowed down. I want to go for as many as possible. Pretty much, as far as any kind of number, I want as many as I can get."

Pitching matchup
BOS: LHP Jon Lester (7-6, 4.35 ERA)
Though Lester stumbled through an inconsistent start to 2009, he comes off arguably his best outing of the year. The lefty allowed just five hits over seven shutout innings on Monday in Baltimore, striking out eight without walking a batter. Especially impressive was the action on his breaking ball, which has gained tightness and depth since doing extra work with pitching coach John Farrell. He seems to have turned a corner, yielding two earned runs or fewer in five of his past six starts.

SEA: RHP Brandon Morrow (0-3, 5.14 ERA)
When the right-hander learns to harness his control, the conversion from reliever to starter could be a much smoother road. Five walks against the Yankees on Tuesday hiked his pitch count to 98 through 4 2/3 innings, and Morrow was removed from the game before qualifying for his first victory of the season. The good news is that Morrow's stamina is at a point where he can reach the 100-pitch mark, but he still needs to get quicker outs.

Tidbits
Saturday's setback snapped a streak of seven consecutive series victories for the Red Sox. Boston had not dropped a set to Seattle at Fenway since Aug. 14-16, 2001. ... Shortstop Jed Lowrie (left knee/left wrist) saw his rehab assignment put on hold Saturday, as Triple-A Pawtucket's home game against Scranton/Wilkes-Barre was postponed due to wet grounds. ... Right-hander Daisuke Matsuzaka (mild shoulder strain) will fly to Fort Myers, Fla., on Monday to begin workouts at the team's Spring Training complex.

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Up next
• Monday: Athletics (Brett Anderson, 4-7, 5.45) at Red Sox (John Smoltz, 0-1, 6.00), 7:10 p.m. ET
• Tuesday: Athletics (Dallas Braden, 6-7, 3.13) at Red Sox (Josh Beckett, 9-3, 3.67), 7:10 p.m. ET
• Wednesday: Athletics (Trevor Cahill, 5-7, 4.55) at Red Sox (Tim Wakefield, 10-3, 4.30), 7:10 p.m. ET