PHOENIX (CBS SF/AP) — For San Francisco Giants fans, it was a bittersweet day. There was Madison Bumgarner smiling about a new five-year contract, but he was wearing an Arizona Diamondbacks uniform.

Bumgarner, who helped the Giants win World Series titles in 2010, 2012 and 2014, decided to leave the Bay Area through free agency, signing a $85 million, five-year deal with one of San Francisco’s division rivals.

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When asked why he chose to make the move, in typical Bumgarner style, the hard-throwing lefthander said it simply came down to winning.

“First and for most it’s about winning,” Bumgarner said. “That’s what the whole decision was based on. And being with a team that in my mind (is playing) my brand of baseball and plays the way I like to play… That’s how I feel about it.”

When asked to expand on his answer, he called the Dbacks lineup a bunch of grinders.

“They (Diamondbacks) just play hard,” he told reporters. “They got a bunch of grinders on this team, guys that don’t take any pitches off. They are just a hard-nosed group of guys.”

Bumgarner has been one of the most feared pitchers at the plate while with the Giants. He has a career .177 batting average with 19 homers, 62 RBIs and 18 doubles. Had he signed with an American League team, his plate appearances would have been limited by the designated hitter rule.

“It was important to me, but it wasn’t a deal-breaker by any means,” he said of signing with another National League squad. “I’ve said it a number of times during my career that I like the National League style of play better…That’s baseball to me.”

Bumgarner has yet to talk at length about his decision with long-time Giants teammates Buster Posey and Brandon Crawford.

“Since all this happened we’ve been pretty busy,” he said. “I talked with a couple of the guys, but it was super quick. We haven’t really gotten into that yet but I’m sure we will.”

When asked about leaving the Bay Area, Bumgarner said he will miss Oracle Park’s vocal fan support.

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“It’s tough. The fans in that city mean so much to me,” he said. “It’s been 10 years there and we won three World championships. Been through a lot together. They have always been as good as they could possibly be to me. I’ll never forget that.”

An hour before his Phoenix news conference, the Giants issued a statement thanking their former star.

“We thank Madison for all that he has given to the Giants and the Bay Area community and we are deeply grateful for the success, excitement and memories he created over a remarkable 11-year period in a Giants uniform,” the statement read. “He played a leading role in all three of the Giants’ World Series championships this decade, but none as memorable as his performance in 2014.”

“We will always cherish his epic 2014 postseason run when he earned both NLCS and World Series MVP honors by carrying the team and all of Giants nation toward a third and historic world championship. He will be forever recognized as one of the greatest pitchers in the 138-year history of the Giants. We wish him and his wife, Ali, all the best as they continue their baseball journey. He is truly a forever Giant.”

Bumgarner’s addition is the marquee move for GM Mike Hazen this offseason. He joins a rotation that also could include Robbie Ray, Zac Gallen, Mike Leake, Merrill Kelly or Alex Young.

It is an intriguing decision for the D-backs, who don’t neatly fit into the category of a small-market or large-market team. They’ve occasionally made splashes in free agency — like when they signed Zack Greinke to a $206.5 million, six-year deal ahead of the 2016 season — but usually are content to have a payroll in the middle of the MLB pack.

Arizona finished 85-77 last season after trading Greinke to Houston in July. Now the D-backs are trying to build a roster that can catch the Los Angeles Dodgers, who won 106 games last season to earn their seventh straight NL West title.

If the D-backs can reach the postseason, Bumgarner’s presence could prove invaluable. He’s best known for his postseason performance — he is 4-0 with a memorable Game 7 save and an 0.25 ERA in World Series play, and has pitched two shutouts in NL wild-card games.

Bumgarner matched his career high with the 34 starts this year, moving past two frustrating, injury-shortened seasons. He won 119 games and has a 3.13 career ERA over 11 seasons with the Giants.

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The four-time All-Star missed nearly three months in 2017 after an April dirt bike accident during an off day in Colorado. Then Bumgarner broke the pinkie on his pitching hand when he was hit by a line drive in his final 2018 spring training start, undergoing surgery to insert pins into the finger. He returned in June that year and wound up 6-7 with a 3.26 ERA in 21 starts and 129 2/3 innings.