Soriano's long ball capped a four-run sixth inning off D-backs starter Rodrigo Lopez (1-1). All of the runs were unearned, as Lopez kept the inning alive when he couldn't corral a high infield popup by Aramis Ramirez.
Starter Randy Wells (3-0) benefited from the most runs the Cubs have scored at Wrigley Field this season. Wells surrendered five runs on eight hits in six-plus innings.
"Just coming away with a 'W' is all I care about," Wells said. "It's a tough day to pitch, and you're conscious of the wind and trying to keep the ball down and trying to keep the ball in the ballpark. Kind of forced me to make some pitches that I wasn't really proud of. All in all, the victory is what matters."
After Wells allowed a leadoff, wind-blown home run to Chris Snyder in the seventh, Piniella made the move to his bullpen. Left-hander John Grabow induced a swinging bunt and struck out two to get out of the inning.
Carlos Zambrano and Carlos Marmol slammed the door on the game's final two frames.
"The story today was the bats and then our bullpen," Piniella said.
For three innings Friday, it looked like the wind was blowing in, as Wells and Lopez did not allow a hit. The only player to reach base before the fourth was the Cubs' Ryan Theriot, the benefactor of a throwing error by Mark Reynolds.
The D-backs took a 3-0 lead in the fourth off three perfectly placed doubles by Stephen Drew, Cole Gillespie and Reynolds, and a sharp-hit single to right by Gerardo Parra. Arizona added to its lead in the fifth on an RBI double by Justin Upton.
The Cubs' first hit of the game came courtesy of a Fukudome home run in the fourth. He ripped a 1-2 slider from Lopez halfway up the bleachers in right field. Fukudome hit the first grand slam of his U.S. career Thursday and now has homers in consecutive games for the first time since coming to America.
Trailing 4-2 in the sixth, the Cubs answered. Theriot extended his hitting streak to 10 games with a line-drive single to right field, and he moved up on a single by Fukudome. One out later, Lopez bumped into Adam LaRoche and couldn't catch a mile-high popup, which loaded the bases. Tyler Colvin hit a sacrifice fly, which set the stage for Soriano's third homer of the season.
The Cubs showed patience at the plate in the seventh to extend their lead to 9-5. An infield single by Derrek Lee and a pair of bases-loaded walks by Ramirez and Soriano plated three runs.
"We were patient," Piniella said. "We made the other team throw strikes, which is good."
Soto led off the eighth with a home run, but he was one-upped on the next pitch by Byrd, who entered the game in the seventh to hit for Grabow.
"We got him in there to pinch hit, and he lined the ball, and then he hit the ball out of the ballpark. I think he hit it out of the stadium. I thought he was going to win that million dollars," Piniella said of the rooftop advertisement beyond Waveland Avenue.
Soto and Byrd were the first pair to hit back-to-back homers since Lee and Ramirez did it Sept. 21, 2009.
With the win, the Cubs capped off April with an 11-13 record, a mark Lee described as "probably not what we expected, not what we were looking for." Even if that record is on par with their 10-11 record in 2009, last year's team was missing one important ingredient: Byrd.
"We're going to start swinging, it's just going to come around," Byrd said. "April's over, so from what I've heard, the Cubs heat up in May. I think it's about that time."