Anthony Rizzo called his first two at-bats a battle. The last one was a whole lot better.

The first baseman capped his return to the Cubs lineup with a walk-off home run in the ninth inning that gave Chicago a 1-0 win over the Cincinnati Reds on Monday night.

Rizzo had missed the last 18 games due to a back problem but led off the ninth by driving a 1-0 pitch from Pedro Villarreal (0-1) over the wall in center field.

Rizzo's homer was his 31st of the season and gave Hector Rondon (4-4) the win after he pitched a scoreless inning of relief.

"The game is over (with) one swing of the bat, and it's a good feeling," Rizzo said.

Thanks to the end of the minor-league season, Rizzo didn't get a chance to go on a rehab assignment before returning to work off some rust. It showed when he struck out against Alfredo Simon in his first two at-bats. He was credited with an infield single in the sixth.

In the ninth, Rizzo looked as though he had never left.

"He certainly made the adjustment in his last at-bat," Cubs manager Rick Renteria said.

Chicago starter Travis Wood didn't get run support and couldn't earn his ninth win despite producing one of his best outings. Wood threw six scoreless innings and allowed three hits.

Simon gave up five hits in seven innings. The Reds right-hander, who is 3-0 against the Cubs this season, was a pleasant first-half surprise but had been struggling recently.

He was 2-7 with a 4.96 ERA in the second half before a strong outing on Monday.

"This is my first season with the Reds to be a starter and I want to show them I can be a starter for a real long time here," Simon said. "I try to finish strong."

He might have earned a win if Cubs center fielder Arismendy Alcantara didn't run down Kristopher Negron's drive to right-center with two outs in the eighth when speedy Billy Hamilton was on first.

"The ball that Negron hit, he absolutely crushed that ball out to right-center," Reds manager Bryan Price said. "Alcantara made a great catch."

Cubs right fielder Jorge Soler went 1 for 3 after he missed a weekend series in Pittsburgh due to the birth of a child.