"I have to play hard just because those kids see me, and I'm the veteran on the team. So I have to show the kids how to play the game," Soriano said.

With the score tied at 3, Reds reliever Sean Marshall (4-4) walked Anthony Rizzo. Just as the skies cleared up, Soriano cracked a two-run shot to center field off Logan Ondrusek.

Shawn Camp (3-5) pitched a perfect eighth for the win and Carlos Marmol worked the ninth for his 14th save in 16 chances.

Todd Frazier and Zack Cozart homered for Cincinnati after the start was delayed by rain for 1 hour, 20 minutes. The NL Central leaders lost their fifth straight but remained 2 1/2 games ahead of second-place Pittsburgh.

It was Soriano's 20th home run. He joined Albert Pujols and David Ortiz as the only active players with 20 or more homers in 11 straight seasons.

"I'm very happy with myself," Soriano said. "I never saw myself as a home run hitter, but 11 years in a row, 20 in a row, I have to be very proud of myself."

Soriano also joined Hall of Famer Andre Dawson as the only players in Cubs history to reach 20 homers in their first six seasons with the club.

"Those kind of guys, they hit. They've always hit," Cubs manager Dale Sveum said. "That's what they were born to do."

Starlin Castro tied it in the sixth with a two-run double off Cincinnati starter Mike Leake. Castro was mired in a 1-for-24 slump before hitting a liner off the center-field wall.

Cubs right-hander Chris Volstad is winless in 22 starts since July 17, 2011. The 25-year-old pitcher allowed three runs and six hits over six innings, including two solo homers.

It took 35 pitches for Volstad to work his way out of a two-run first inning.

Cozart greeted Volstad with his fourth leadoff home run, capping an eight-pitch at-bat. It was his 13th of the season.

Frazier took Volstad deep in the fourth for his 14th homer of the year.

Volstad let at least one runner aboard in each inning he pitched, but managed to escape with a quality start.

"We scored early and kind of cruised for a while and when you do that, any team is going to make a run," Cozart said. "They got a couple of big hits by Castro and Soriano, and we didn't."

Leake was charged with three runs in six innings. He struck out five and walked two.

"The one pitch to Castro kind of beat me," Leake said.

The right-hander cruised through five innings before Castro came through with runners on first and third. Leake had given up nine runs in his last two starts, a span of just 7 2/3 innings.

"Nothing mentally changed," Leake said. "I just wasn't attacking them."

Rizzo got the Cubs on the board in the first with an RBI single to score David DeJesus.

Rizzo reached base four times, including a double to lead off the fourth, but the 23-year-old slugger was too aggressive on the basepaths and was thrown out at third trying to advance on Soriano's groundout.

Former first-round draft pick Brett Jackson went 0 for 3 in his home debut for Chicago.

Game notes
Cubs C Steve Clevenger was ejected in the fifth for arguing balls and strikes. ... Chicago RHP Matt Garza, out indefinitely with a stress reaction in his right elbow, wants to pitch again this season. "I'm hoping to, that's why I'm working my tail off to get back," he said. ... The Reds activated C Devin Mesoraco (concussion) from the 7-day disabled list and optioned C Dioner Navarro to Triple-A Louisville. ... Homer Bailey (9-7, 3.98 ERA) pitches Friday for Cincinnati against Justin Germano (1-1, 3.38) in the second game of the four-game set.