"It's a good feeling," Jackson said about turning the game over to the bullpen. "We have confidence in those guys. We're confident that they're going to come in and pick up the slack."
With the score tied 3-all in the fifth, the Cubs loaded the bases with no outs against reliever Nick Christiani (0-1). Mike Olt hit into an RBI forceout, and Schierholtz followed with a sacrifice fly.
Manager Rick Renteria wasn't surprised to see his Cubs string together productive at-bats.
"We've been having a tough time trying to tack on runs and score runs," he said. "Today was an example of what we can do.
"It was a good day all around," the first-year manager added. "(Jackson) kept us in the game and the relief pitching did a nice job."
Schierholtz added a two-run single off Sean Marshall against a drawn-in infield in a four-run ninth.
"It was good to see Nate get a hit there," Renteria said.
Chicago needed just three batters to take a 2-0 lead in the first on Emilio Bonifacio's leadoff single and the left-handed hitting Rizzo's 426-foot, opposite-field homer to left-center off left-hander Tony Cingrani.
"It's really early," Rizzo said. "I'm just trying not to do too much, especially against left-handers. I'm not trying to get three hits in one at-bat."
Todd Frazier tied the score with a two-out, two-run double in the half.
Pena, signed by the Reds as a free agent in November, gave the Reds a 3-2 lead when he homered leading off the second -- his first home run since Aug. 11. His previous NL homer was for Atlanta against the Marlins on April 13, 2007.
Castro's single tied the score in the third.
Cincinnati starter Cingrani gave up three runs and six hits in four innings.
"I'm just a little fatigued," said Cingrani, whose velocity noticeably dropped in his last inning. "I was laboring. I don't know what it is about the first inning. I've just got to pitch."
Cingrani denied that he was having back problems, which forced him to spend time on the disabled list last season.
"My back is fine," he said. "I'll make some minor adjustments and see how it goes."
Manager Bryan Price believes his left-hander is simply in a slump.
"Cingrani wasn't real sharp," he said. "His velocity started to back down that last inning. I didn't think we should send him back out there and expect different results. Other than his first starts against St. Louis, he's been finding his way. We just want to make sure he's strong. He hasn't been sharp lately."
Brandon Phillips had an RBI single in the fifth, his eighth hit in his past 46 at bats (.174).
Reds manager Bryan Price confirmed that LHP Aroldis Chapman will start and pitch one inning for Class A Dayton on Thursday in the first game of his minor league injury rehabilitation assignment. Price expects Chapman to make four appearances over seven to 10 days in the minors. Chapman had a plate inserted above his left eye to heal fractures from a line drive on March 19. ... The Cubs are scheduled to open a five-game homestand Friday against St. Louis. The Reds are scheduled to open a four-game home series Thursday against Milwaukee, the team with the big leagues' best record.