SAN DIEGO — North Side, South Side, Chicago has become the center of baseball at the winter meetings.

The Cubs struck the first big deal among top free-agent pitchers, agreeing Tuesday night to a $155 million, six-year contract with left-hander Jon Lester.

"It's not often you get to win the lottery, and we won the baseball lottery this year," new Cubs manager Joe Maddon said. "Now it's up to us to put it into effect."

After losing 188 games over two seasons, the White Sox acquired starting pitcher Jeff Samardzija — a former Cub — from the Oakland Athletics as part of a six-player trade Tuesday. That came hours after they reached a $46 million, four-year deal with closer David Robertson.

"In our mind we're not finished yet," White Sox general manager Rick Hahn said. "We still know we have some other areas we need to improve and we're hopeful that in the coming days, and if not the coming days, then the coming weeks, we'll be able to fill a couple more voids in our roster."

On the South Side, the White Sox won the title in 2005 for their first championship since 1917.

The long-suffering Cubs are seeking their first World Series title since 1908.

They gave Lester a deal with an option for 2021 that, if it becomes guaranteed, would make the contract worth $170 million over seven seasons. The average annual value of $25.8 million is the second-highest for a pitcher behind Clayton Kershaw's $30.7 million as part of a $215 million, seven-year deal with the Los Angeles Dodgers that began this year.

A three-time All-Star who turns 31 next month, Lester won two World Series titles with Boston. Now he's in position to throw the first pitch of the 2015 season, at Wrigley Field against St. Louis on April 5.

Earlier Tuesday, the Cubs acquired All-Star catcher Miguel Montero from Arizona for minor league right-handers Jeferson Mejia and Zack Godley — a deal that added $40 million in payroll over the next three years. Chicago has a pending $20 million, two-year deal with right-hander Jason Hammel, traded by the Cubs to Oakland last summer.

Maddon had been used to small payrolls in Tampa Bay.

"I've not been on this side since my days with the Angels, when I got an email in Italy that we had signed Vladimir Guerrero," said Maddon, who was a coach in Anaheim before switching to Tampa Bay. "I think that definitely sends that message how Theo (Epstein) and the group feel about this particular group. But understand, we have a lot of young players that have to grow up as quickly as possible. But having Jon there adds to the flavor and the possibility."

Lester's deal should lead to more intensive negotiations involving teams interested in free-agent pitchers Max Scherzer and James Shields. Lester also had been sought by Boston, World Series champion San Francisco and the Dodgers.

In the day's other moves, the Pittsburgh Pirates agreed to a $39 million, three-year deal to keep left-hander Francisco Liriano. And Atlanta agreed to a one-year deal with free-agent infielder Alberto Callaspo.

The deals for Robertson, Liriano and Callaspo were disclosed by people familiar with the negotiations who spoke on condition of anonymity because they had not been announced.

Samardzija played football for Notre Dame before pitching for the Cubs.

"Being a Chicago guy, that's one of the craziest things I've thought about," he said. "I'm sitting here thinking, 'Now, do I really have to go get my cleats on and go play for the Bears?' If I could skate, maybe the 'Hawks. My jumper's garbage, so the Bulls are out of the question."

Trading an All-Star for the third time in less than two weeks, the Athletics sent Samardzija and right-hander Michael Ynoa for right-hander Chris Bassitt, catcher Josh Phegley and first baseman Rangel Ravelo and infielder Marcus Semien.

Samardzija was 31-42 with a 3.97 ERA for the Chicago Cubs from 2008 until July 5, when he was traded to the A's. He went 5-6 with a 3.14 ERA for Oakland. He can become a free agent next autumn.

Earlier in the offseason, the White Sox agreed to a $25 million, two-year contract with first baseman Adam LaRoche and a $15 million, three-year deal with left-hander Zach Duke.

"We're going to make every effort to make this a long-term relationship," Hahn said. "We felt that this was a premium starter who fit, not just in terms of how he fit in our rotation, but how he fit in our clubhouse."

Samardzija wasn't so sure he would want to miss free agency.

"You're so close to it, you really want to experience it," he maintained. "But like I said before, when the situation's right, it's right. When the numbers are right, they're right."