Boston’s J.D. Drew throws his bat after striking out with two men on base to end the second inning last night.

AP / Tom Mihalek

PHILADELPHIA — Bartolo Colon, who had to leave his start on Monday night because of a lower back strain, was placed on the disabled list yesterday.

He was replaced on the roster by Chris Smith, a right-hander called up from Pawtucket. Smith will provide manager Terry Francona with another arm out of the bullpen for three games. It is expected that Smith will be returned to Pawtucket on Saturday, when Daisuke Matsuzaka will be activated for a start at home against St. Louis.

Colon suffered the injury during one of his overly aggressive swings — the force of one caused his helmet to fall off. Colon whiffed both times.

The corpulent right-hander pitched the fourth, but Francona said he and pitching coach John Farrell saw a change in his arm angle and didn’t want him to risk further injury.

Colon spent time on the DL in 2006 because of a rotator cuff injury, and was on it last year because of elbow woes. He had been shut down once this year because of an oblique muscle strain.

But the veteran has gone 4-2 for the Sox. So the feeling of Francona and the organization is a better-safe-than-sorry philosophy.

“We’re being somewhat cautious not only with him, but all of our pitchers,” said Francona. “We want them to be healthy and productive, and we think that goes hand in hand. We want to have him all year.”

Colon’s injury, plus the serious foot injury suffered by the Yanks’ Chien-Ming Wang, has caused more debate about the fears American League managers have during interleague play in National League parks where the designated hitter is not used.

“I know anyone can run the bases. [Wang] was just bad luck. You’re asking people to do stuff [hitting, running the bases] they’re not used to doing. That’s difficult,” said Francona.

Rotation juggled

Colon’s injury forced the Red Sox to make alterations in their starting rotation.

Some of the changes had been planned, notably extra rest for Josh Beckett, but Colon’s injury likely has spared rookie right-hander Justin Masterson a return trip to Pawtucket.

Boston enjoys a day off tomorrow, making it easier to give Beckett a breather. So the starters for this weekend’s series at Fenway Park against the Cardinals will be Tim Wakefield (Friday ), Matsuzaka (Saturday ) and Jon Lester (Sunday).

Lester will slide up into Beckett’s spot for the Sunday outing. Lester, who started last night against the Phillies, will be pitching on the normal four days’ rest.

Beckett will pitch Monday night in the opener of a three-game series against Arizona at Fenway. He’ll be pitching on seven days’ rest.

Francona said there is nothing wrong with Beckett physically.

Around the bases

David Ortiz was able to do some range-of-motion exercises yesterday with his injured left wrist now that his hard cast has been taken off. Francona said the medical staff is pleased with the slugger’s recovery. . . . Kevin Youkilis (back) missed his second straight start and, given the fact the Sox have tomorrow as a day off, he might be held out of the lineup today even if he’s feeling better. . . . The Sox extended their player development contract with Single-A Lowell for two more years, through the 2010 season . . . Boston signed Notre Dame right-hander Kyle Weiland, the Sox’ second third-round pick, as well as catcher Christian Vazquez of the Puerto Rico Baseball Academy High School, a ninth-round selection.

skrasner@projo.com