Just like that, the Boston Red Sox have a starting rotation again.

One day after acquiring a pair of starters, the Red Sox picked up a third, rebuilding their starting rotation this offseason almost as quickly as they took it apart during the summer.

Hours after trading for Detroit righthander Rick Porcello on Thursday, Boston signed righty Justin Masterson as a free agent. On Friday, the Red Sox acquired lefty Wade Miley from Arizona for righties Rubby De La Rosa and Allen Webster and infielder Raymel Flores.

"We're in a position where everyone knows we need to add quality starting pitching," general manager Ben Cherington told reporters on the team's second conference call of the night. "We've been able to acquire the three starters we have this week while really being able to maintain the top end of our young pitching."

The Red Sox won the World Series in 2013 with a rotation that included Jon Lester, John Lackey, Jake Peavy, and Felix Doubront. By midsummer it was obvious the team would not successfully defend its title in '14, and Cherington traded them all away to start planning for the future.

Masterson, Porcello, and Miley will join holdover Clay Buchholz and one of Boston's young arms - perhaps Anthony Ranaudo or Brandon Workman - in a rotation that is so far lacking an ace.

Masterson isn't sure they need one.

In a separate trade Friday, Boston obtained Zeke Spruill from the Diamondbacks for Myles Smith in a swap of righthanders.

Cubs: Lester deal official

The Chicago Cubs officially announced the signing of new ace Jon Lester.

The Cubs said Saturday that Lester had joined them. They are scheduled to introduce him at a news conference Monday at Spiaggia Restaurant, a favorite of President Obama's family.

Lester agreed Tuesday night to a $155 million, six-year contract with the Cubs. His contract contains an option for 2021 that, if it becomes guaranteed, would make the deal worth $170 million over seven seasons.

Harper a no-show

Washington Nationals general manager Mike Rizzo said the club was "disappointed" outfielder Bryce Harper did not show for the NatsFest fan festival.

In a statement e-mailed by one of his agent's employees, Harper said: "I have attended NatsFest each year and always enjoy my experience with the fans, but was unable to attend this year's event due to matters out of my control. I look forward to next year's NatsFest."

The Major League Baseball Players Association has filed a grievance on Harper's behalf over whether he should able to void the 2015 terms in the final season of a $9.9 million, five-year contract he signed when drafted. An arbitration hearing could happen next week if the case isn't settled.

Rizzo said Saturday: "We're disappointed he's not here, but he chose not to be here because of the grievance."

Outfielder Jayson Werth met with fans but, unlike other players present, did not speak to the media.

"That was my decision," Rizzo said.

Werth was convicted this month of reckless driving and sentenced to 10 days in jail.