MESA, Ariz. -- Jeff Samardzija made a strong spring debut and the Chicago Cubs scored four unearned runs in the first inning against San Francisco Giants ace Matt Cain, then held on for a 4-3 victory Sunday at HoHoKam Stadium.

Cubs catcher Dioner Navarro, acquired as a free agent during the winter, hit a three-run homer in the first inning after Alfonso Soriano hit a line drive off the right leg of Cain and reached first as the ball caromed away. Giants first baseman Brandon Belt made a throwing error one batter earlier.

"We were a little concerned," Giants manager Bruce Bochy said. "The knee started to swell a little bit. We were a little cautious with the knee. He wanted to get back out there, but we shut him down."

Cain, who finished the inning but did not take the mound in the second, said getting hit had nothing to do with giving up the home run, and said he expects to make his next spring start on schedule.

"It should be fine," said Cain, who has been tabbed by Bochy to make his first career opening-day start for the defending World Series champions. "Just some ice now. Nothing to worry about, I don't think.

"Maybe I've just got to start using my glove more -- or actually USING my glove."

All four runs allowed by Cain were unearned because of a one-out throwing error by first baseman Brandon Belt one play before Soriano's drive.

"The best thing is that he's OK," said Soriano, who also singled to left-center in the third. "That makes me happy."

Samardzija gave up one run on three hits without a walk in his two innings of work, striking out two.

"I was happy with how things went," he said. "The no walks and fastball command was important."

Considered a front-runner for the Cubs' opening-day start, Samardzija escaped far worse injury than Cain sustained. He ducked and stumbled to avoid by inches Guillermo Quiroz' drive toward his head in the second inning.

An inning earlier Kensuke Tanaka got Samardzija with a glancing shot on another shot up the middle -shortstop Starlin Castro turned the carom into an out.

"Both of them were about as close as they get," Samardzija said. "That's part of the fun. You've got to be on your toes, be ready to go. It's better if you knock it down and get an out like the first time."

Last week while pitching batting practice to teammates, Samardzija was nearly hit another time when second baseman Darwin Barney hit a one-hop shot back through the box.

"After the second time (Sunday)," Navarro said, "I went out there and asked him where the magnet was."

Giants third baseman Pablo Sandoval, the World Series MVP, continued his strong hitting from winter ball, going 2 for 3, including a run-scoring double off Cubs closer Carlos Marmol in the third.

Sandoval, who duplicated his postseason MVP effort in the Venezuelan League finals last month, started both of the Giants' first two spring games (3-for-5, 2 RBIs).