Given the past history of Edwin Jackson and the bullpen, it seemed wise that the Chicago Cubs were carrying 13 pitchers entering Thursday's game against the Arizona Diamondbacks.

After a rough start, Jackson settled down to retire 17 of the final 18 batters he faced. But the Cubs were limited to five hits by rookie Mike Bolsinger and three relievers in a 5-2 loss.

Jackson, who hadn't pitched past the sixth inning in any of his first four starts, allowed an RBI double to Miguel Montero in the first.

Jackson put the first three batters on base in the second but escaped with only two runs allowed as Gerardo Parra grounded into a double play.

Emilio Bonifacio manufactured the Cubs' run in the first when he slid around the tag of Aaron Hill for a double and scored on a fielding error by left fielder Roger Kieschnick.

The Diamondbacks scored two more runs in the eighth off embattled reliever Jose Veras. Anthony Rizzo hit a solo home run off left-hander Oliver Perez in the bottom of the eighth.

The Cubs' bullpen currently features four pitchers who have made 10 appearances or more in their first 20 games.

Pedro Strop's failure to hold a three-run lead Wednesday was just another reason why the Cubs elected to promote left-hander Zac Rosscup and Neil Ramirez from Triple-A Iowa.

"We want to be mindful of not overtaxing all of our young guys or any of the guys in the pen," manager Rick Renteria said.

Renteria remained hesitant to name a closer. The bullpen was thought to be a strength but has a 4.06 ERA.

"There are different variables and scenarios that play out," Renteria said. "But I still feel very confident in the arms we have.