By Jeremy Harness

AP photo: Former Chicago Cub Jeff Samardzija throws in the first inning for the San Francisco Giants against the Cubs at Wrigley Field to open the four game series on Thursday night

The Giants’ bullpen has been shaky for a better part of the season, and it was victimized again Thursday night.

After Jeff Samardzija was forced out of the game after pitching only four innings, the Giants could not hold on to a slim one-run lead, and as a result, they fell to the Chicago Cubs, 5-4, within the confines of Wrigley Field.

The first three innings proved to be explosive on the offensive end. Hunter Pence got things started in the first inning with a two-run homer off Cubs starter Mike Montgomery.

However, Chicago came to the plate in the bottom half of that inning and pounced right on Samardzija, who was making his return to Wrigley Field after starting his career with the Cubs. Three runs were scored off the Giants right-hander in the inning, with singles by Kris Bryant and Jason Heyward as well as a double by Chris Coghlan doing the damage.

Samardzija rallied and even helped himself at the plate, as in the second inning, he got a fly ball deep enough to bring Joe Panik home and tie the game. One inning later, a throwing error by second baseman Ben Zobrist allowed Buster Posey to score on Brandon Crawford’s fielder’s choice, giving the Giants the lead.

However, that would not last.

Samardzija was able to settle down for the next three innings after giving up the three-spot and keep the Cubs from scoring any more runs while he was in the game. However, by the end of the fourth inning, he had already thrown 87 pitches, and it was time for manager Bruce Bochy to go to the bullpen.

Things were going smoothly until the seventh inning, when Addison Russell hit a two-run single off reliever Cory Guearrin to give Chicago a lead that it would not relinquish.

As a result, the Giants fell behind the Los Angeles Dodgers by one more game, and they are now two games back of the National League West leaders.

The Giants have three more games in Chicago before heading to Colorado and Arizona for three-game series against the Rockies and Diamondbacks, respectively.