The rally came after the Rockies had scored six in the top of the inning to erase an 8-3 Chicago lead.
"You see two-run comebacks in the bottom of the ninth inning, but you don't see too many after you give up six in the top half of that inning," Cubs manager Lou Piniella said.
With the Cubs trailing 9-8 in the ninth, Mark DeRosa led off with a bloop single to center, and was replaced by pinch-runner Felix Pie. Angel Pagan struck out, and Rob Bowen hit into a fielder's choice, forcing Pie at second.
Pinch-hitter Koyie Hill singled to left, advancing Bowen to second, and he was replaced by pinch-runner Jacque Jones.
Ryan Theriot then hit a ground ball to second baseman Kazuo Matsui that should have ended the game. But Matsui bobbled it, and everybody was safe and the bases were loaded.
"I'm frustrated for that last play -- I feel sorry for that play," Matsui said through interpreter Yoshita Ono. "It's my first error. I was working on defense. That's why I didn't make any errors until today.
"It hopped a little bit, but it's an error," Matsui said. "No excuse for that."
The stage was set for Soriano, who was 0-for-5 in the game. Soriano took Brian Fuentes' first pitch for a ball. Soriano drove the next pitch to center field, driving in Jones and Hill for the game-winner.
"The way Soriano has been swinging the bat, it's hard to feel like you don't have a chance," Hill said.
Soriano hit .480 in the Cubs' last six games with four home runs to win NL Player of the Week honors.
The game should've been over earlier. Scott Eyre was on the mound in relief for the Cubs, who were shorthanded without closer Ryan Dempster for the third straight game.
Matsui singled to lead off, Matt Holliday walked and Todd Helton doubled to score Matsui, and force Piniella to call upon Bob Howry, who had pitched the last two games.
Howry (4-4) gave up RBI singles to Garrett Atkins and Brad Hawpe to close to 8-6. Rookie Troy Tulowitzki swung at Howry's first pitch and launched it into the bleachers for a three-run homer and 9-8 lead.
The game was halted momentarily when a fan ran onto the field toward Howry. Security guards tackled the man before he could reach the pitcher, and escorted him off the field.
It just added to the craziness.
Lost in the late-inning drama was Mike Fontenot's 5-for-5 effort. He tied the team's single-season high for hits in a game, and also extended his hitting streak to a career-high eight games.
"How about 5-for-5 for this young man?" Piniella said. "Pretty impressive, isn't he? He's telling me he wants to stay in the lineup."
"I'm happy to [be overshadowed]," Fontenot said. "I'm glad we came out and won the ballgame in grand fashion."
The Cubs won their fourth straight, and appear to be on a roll.
"We had this one in hand and it got away from us there in the ninth," Piniella said. "Then we snatched it right back in our bottom half. It's a great win. You couldn't script it any better."