They are the two top teams in the American League, titans of the AL East and AL West.
The Red Sox (57-37) own the most wins in baseball, while the A's (54-38) are 111-64 since July 1 of last year -- the best mark in the Major Leagues over that span.
The two will square off starting Friday at O.co Coliseum in each team's last series before the All-Star break.
Oakland has clinched a winning record before the All-Star break for the first time since 2008. Its 54 wins already tie the 2003 squad for the most by an A's team at this point in the last 25 years.
Boston's 57 wins are tied for most in club history to this point in the season with the 1978 Sox (57-26).
John Lackey will look to maintain Boston's grasp of the division lead. The right-hander has been dominant the past few weeks and has called this season the best first half of his career. Opponents are hitting .243 against him, and he has lasted at least seven innings in each of his last five starts.
"The last three outings it looks like his arm strength continues to build," manager John Farrell said. "We are seeing some velocities on the board that we haven't seen in quite a while from him. Once again, very good command, a lot of strikes. An outstanding performance on his part."
Oakland is a familiar foe for Lackey, the longtime Angel. He leads all active pitchers in winning percentage against the A's with an 18-6 record. He has a 2.91 ERA vs. them.
Jarrod Parker, meanwhile, received a no-decision after allowing three runs (two earned) on five hits and three walks over 6 1/3 innings against the Royals last Saturday. It was his first start since exiting a game early on June 29 with tightness in his right hamstring.
Parker is on a career-high-tying four-game winning streak over his last eight starts, with a 2.24 ERA during that span.
Red Sox: Buchholz in line to rehab Sunday
Injured starter Clay Buchholz is on schedule to make the first of at least two rehab starts on Sunday, though the location has yet to be determined.
He's scheduled to throw about 45-50 pitches.
"That would be the target," Farrell said. "With that being the case, the next start is going to have to be a progressive step from there just so we're not overtaxing the pen once he returns.
A's: Gray added to bullpen
Tuesday was a wakeup call Sonny Gray did not mind getting in the morning hours after a night game in Colorado Springs.
There was a banging at the door of his hotel room shared by Sacramento teammate and roommate Andrew Werner at 10 a.m. on Tuesday. Naturally, both assumed it was housekeeping.
"We were yelling, 'Go away!'" Gray said. "Then we finally opened the door."
It was Gray's manager Steve Scarsone telling him he had been called up by the A's.
"It was really exciting," Gray said Wednesday in front of his locker at PNC Park, before the A's 5-0 series-ending loss vs. the Pirates. "It was completely unexpected, and I think that's what made it even more exciting. He let me know and told me to go out and call my mom."
Gray did just that, relaying the news to mom Cindy Craig, who was in Florida on vacation, before prepping for a flight to Pittsburgh to join the A's and prepare for a new role out of the bullpen.
Gray's promotion, which resulted in the optioning of Dan Straily, came 765 days after the A's picked him with their first pick in the 2011 First-Year Player Draft. Through 16 starts with Triple-A Sacramento, he was 8-5 with a Pacific Coast League-leading 2.81 ERA.
Gray will pitch out of the bullpen for now, a role he held for a short time in college and also experienced in Spring Training. He pitched two scoreless innings in Wednesday's loss.
• David Ortiz is one homer shy of 20 for the season, which would mark his 11th 20-homer season with Boston, tied with Dwight Evans and Jim Rice for second-most in club history. Ted Williams leads the pack with 16 seasons with at least 20 homers.
• After going homerless with a .258 average in May, Jed Lowrie is hitting .309 with three homers since the start of June.
Jeff Kirshman is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.