Beckett, who had last pitched Aug. 17 due to right elbow inflammation, started Friday night against Texas.
Lowell was back in the lineup for the first time since Aug. 12 after being sidelined by a strained right oblique muscle. Casey didn't start, but was available for the first time since Aug. 19 after being out with a neck strain.
"I felt really bored," Lowell said. "I wanted to be back playing every day. I was anxiously awaiting the chance. We're playing good and this is the exciting time of the season."
The Red Sox entered 3½ games behind Tampa Bay in the AL East, but had a 5½-game lead over Minnesota in the wild-card race.
"This is what it's all about. You play the whole year to be in this spot in September," Casey said. "It's a lot of fun. I'm excited to be a part of it."
First baseman Kevin Youkilis remained in Boston on Friday tending to a personal matter. But manager Terry Francona said Youkilis, who received treatment in Boston for back problems on Thursday, would rejoin the team Saturday. Youkilis has missed five of six games, including two due to illness and two more because of back spasms.
Outfielder J.D. Drew, who hasn't played since Aug. 17 because of a strained lower back, took batting practice and caught balls in the outfield on Friday, the first time he's done both since going on the disabled list.
"It seems like he takes a step forward and one back, so we'll see where he's at," Francona said. "He's hoping he's only a couple, three days away, but [not] until it goes away."
The Red Sox outrighted right-hander Eric Hull to Triple-A Pawtucket. Hull was designated for assignment on Aug. 30.