Justin Masterson will start for the Sox tomorrow, taking the spot vacated by Clay Buchholz.

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The Providence Journal / Mary Murphy

BOSTON — Never mind a five-man starting rotation. Because of injuries and other problems, the Red Sox are about to play “starter for a day” and bring in a new guy to start both tomorrow and Wednesday.

Justin Masterson will start tomorrow against Kansas City, manager Terry Francona said yesterday. A day later, he will return to Portland and be replaced on the roster by Bartolo Colon, who will make his Red Sox debut Wednesday.

Masterson, in effect, will take the spot vacated by Clay Buchholz (DL-finger), while Colon, with an extra day of rest, will pitch so that Daisuke Matsuzaka doesn’t have to pitch on short rest.

Matsuzaka would have been slated for Wednesday, but after Friday’s rainout, pitched Saturday and would have been going on three days’ rest.

The expectation is that Colon will remain in the rotation with Buchholz sidelined. Francona acknowledged that Masterson has been cuffed around in his last few starts for Double-A Portland after making one excellent emergency start for Boston.

He said the pitcher’s mistake has been leaving balls up in the zone late in games.

Colon will be the 35th player and 18th pitcher to be used by the Sox.

All last season the team needed 40 players, 20 of them pitchers.

Ellsbury’s streak ends

Jacoby Ellsbury was caught stealing in the fourth inning, ruining his perfect record on steals.

He had been successful on his first 25 attempts, including 16 this year, the most to begin a career in team history.

The Brewers called a pitch out and got Ellsbury on a perfect throw by catcher Mike Rivera.

“They picked the right pitch,” Francona said.

Ellsbury said he noticed Rivera step out for a pitchout.

“I’ve already gained 20 feet by the time the catcher is moving out,” Ellsbury said.

“If I stop I’m probably in a rundown unless they throw the ball away. But it took a perfect catch and a perfect throw. Give them credit.”

“If you steal enough, you’re going to get caught eventually,” he said.

He admitted it was a weird feeling being out.

“I didn’t know what to do,” he said.

Beckett’s wanderers

Josh Beckett won for the third time in the last four starts and improved to 5-3, but his outing wasn’t without some concerns.

Beckett was victimized for four homers — two by Ryan Braun, and one each from Prince Fielder and J.J. Hardy — the most since he allowed four on May 30, 2006, against Toronto.

In his last four starts, Beckett has allowed seven homers.

“A few balls wandered over the middle of the plate,” Francona said, “especially early on. He left some pitches over the plate to good hitters.”

Said Beckett, “Guys swung the bats well (against me) today. I just try to focus on positive things. I made some good pitches, made some poor pitches. I threw a lot of strikes and sometimes strikes get hit, especially when they’re not good strikes, down in the zone.

“At the end of the day, we won, and that’s what we’re trying to do. We’re fortunate that I gave up some runs but we scored more than they did.”

It seemed every homer hit off Beckett was on a hanging breaking ball, indicating location and execution were issues.

“I think anytime somebody hits a home run on a breaking ball,” said Beckett, “it’s probably the pitcher’s fault because if it’s down, it’s hard to hit.”

Still, Beckett managed to strike out nine and has now struck out five or more in each of his last 13 starts, the longest such streak since Pedro Martinez put together a streak of 14 straight from July 1-Sept. 14, 2004.

Smith in the bigs

Chris Smith, in his seventh professional season, finally heard the words every player wants to hear when he signs.

You’re going to the big leagues.

Pawtucket manager Ron Johnson gave the 27-year-old right-hander the good news around midnight on Saturday in Scranton. The Red Sox needed a fresh arm in the bullpen, and Smith was called up to fill the role, so he drove from the Scranton-Wilkes Barre area, where the PawSox were playing, to Allentown for flights to Philadelphia and then Boston, arriving at the Sox’ clubhouse around 11:45 yesterday morning, less than two hours before the first pitch.

Smith almost didn’t know how to react when Johnson told him of the promotion, thinking back to the promise of making it big in the majors when he was drafted in the fourth round in 2002 through all the injuries and rehabs he had had to endure since then.

“I got real cold all of a sudden and broke out in a sweat,” said Smith after the Sox’ 11-7 win over the Brewers yesterday.

“I had mixed emotions. It took a while for it to sink in. I was so excited. All the emotions hit me at once. It happened so fast. It had been such a long road. I broke down and cried. I called my mom and my sisters, and they started crying.”

Smith wasn’t told how long he’ll be in Boston. The reality is that Smith, who did not pitch yesterday, will probably be here only through tonight’s game because the Red Sox will have to make a move to add Masterson for a start tomorrow night against Kansas City.

Moss feeling better

Outfielder Brandon Moss, who underwent an emergency appendectomy a few weeks ago, will get some at-bats in extended spring training today and tomorrow, then join the PawSox in mid-week. “He’s ready to go,” said Francona, who added that veteran outfielder Bobby Kielty (broken hand) remains at home in California.

smcadam@projo.com