SAN FRANCISCO -- The Cubs lost 9-1 to the San Francisco Giants on Thursday afternoon. Here's a quick look at the game.

How it happened: The Cubs got on the board first when Starlin Castro doubled home Anthony Rizzo in the second inning, but the Giants quickly tied it in the bottom of the inning then took the lead for good in the third, scoring four runs. The big blow was a three-run home run from Marlon Byrd to dead center off starter Dan Haren. Kelby Tomlinson hit a grand slam off reliever James Russell in the eighth to seal the deal for San Francisco. Giants starter Madison Bumgarner didn’t give up a hit after the second inning, striking out 12 in six innings. Haren gave up five runs on six hits and had three walks in 6⅓ innings.

What it means: The combination of Bumgarner and some defensive holes sealed the fate for the Cubs early in this game. A Kyle Schwarber throwing error from behind the plate added stress to the Cubs in the Giants' big third inning, and Matt Szczur couldn't track down a fly ball the inning before. Haren needs every advantage he can get, as this series was a reminder that the Cubs need better defense when the back end of their rotation is on the mound -- especially in a spacious ballpark such as AT&T Park.

It's hard to be too critical of the offense as Bumgarner, the 2014 World Series MVP, isn't exactly easy to hit at home, where he has a 2.05 ERA this season. The Cubs needed a low-scoring game Thursday to have a chance, but the combination of Byrd's home run and the Cubs' defense took care of that idea. Meanwhile, Russell has given up nine runs in his last 3⅔ innings.

Another homer against Haren: There will be fan rumblings to replace Haren in the rotation after he gave up his major-league-worst 29th home run this season. His ERA in a Cubs uniform rose to 6.79.

Fowler day-to-day: Dexter Fowler had an X-ray taken of his shin, but it was negative. He's day-to-day. The Cubs say it's not a serious injury, but his status for Friday's game is unclear.

What's next: The Cubs move down the coast to Los Angeles, where they will face the NL West-leading Dodgers the next three days. Jason Hammel (7-5, 3.35 ERA) takes on Clayton Kershaw (10-6, 2.29) on Friday at 10:10 p.m. ET.