The last time Edwin Jackson's teammates gave him a comfortable cushion, he let it slip away.

The Chicago Cubs right-hander was determined to not let that happen again — and he personally helped make sure it didn't. He capped the Cubs' offensive outburst with a solo homer in the seventh as Chicago rolled to a 9-1 victory over the suddenly punchless Cincinnati Reds.

Welington Castillo drove in three runs with two home runs — his first career multi-homer homer game — and Donnie Murphy added a two-run shot as the Cubs kept adding on after taking a 5-0 lead through three innings.

"The last time my team scored a lot of runs, I gave it up," Jackson said, referring to an 8-6 loss at San Diego on Aug. 23 in which the Cubs led 6-0 before he stepped on to the mound. "I said, 'That is not going to happen again.' (The Reds) had men on base in a lot of innings, but I was able to get out of it."

Jackson hit his second career home run in the seventh inning on his way to his first win in seven starts since July 31. The Reds — who went into the game third in the NL Central, two games behind first-place St. Louis — saw their streak of consecutive scoreless innings reach 15 since a walkoff win over Los Angeles on Sunday. Then Zack Cozart and pinch-hitter Corky Miller hit consecutive doubles with one out in the seventh.

Jackson (8-15) allowed nine hits and one run with four strikeouts in seven innings.

The Cubs earned consecutive wins over Cincinnati for the first time since 2011, when they won on Sept. 7 in Chicago and Sept. 12 in Cincinnati — a span of 36 games. They clinched their first series win at Great American Ball Park since Aug. 3-5, 2009.

Losing two to the last-place Cubs right after taking three out of four from the Cardinals and sweeping the West Division-leading Dodgers left outfielder Ryan Ludwick mystified.

"We played two good teams and played really good baseball," Ludwick said. "I don't know if you can call it a letdown. I don't know if you call it not focused. I don't know if you call it not enough energy. I don't know if you call it those guys came in to play spoilers. All around it was a bad game from the first inning on. I can't get a grip on it. I don't think anyone wanted to lose two to the Cubs. They're a major league team, but they're in last place, and we're trying to chase down a couple of teams in front of us."

Reds starter Tony Cingrani, in his second start since coming off the disabled list on Thursday, left the game two outs into the second inning with back spasms. He had been sidelined since August 25 with a lower back strain.

"It was the same injury to Cingrani," manager Dusty Baker said. "He warmed up great. He didn't feel anything. In between the first and second, he said his back was tight. It was devastating at that point. We had to go to the bullpen early. Thankfully, we have a day off on Thursday. The back end of my bullpen was beaten up pretty badly."

Junior Lake led off the second with a double, giving him a seven-game hitting streak and his fourth streak of seven or more games since he was called up from Triple-A Iowa on July 19. Castillo followed one out later with a 470-foot homer into the upper deck in left field on a full-count pitch. Castillo's fifth homer of the season was his first since Aug. 10. Cingrani (7-4) left the game one out later.

"I don't think I've hit a longer one," Castillo said. "I hit it a long way."

Murphy added his 377-foot, two-run homer down the left field line on the first pitch he saw from Greg Reynolds in the third inning. Lake singled to right and went to second on right fielder Jay Bruce's error, and Darnell McDonald drove him in with a soft single to center field that Shin-Soo Choo appeared to midjudge.

Barney drove in Jackson with a sacrifice fly in the fourth and Murphy added an RBI double in the sixth before Castillo hit his second homer in the seventh.

"It was nice to (Castillo) have his first two-homer game," Chicago manager Dale Sveum said. "He hit the big home run early that set the tone."