With one out in the Chicago first against Bronson Arroyo, Marlon Byrd singled and scored on Ian Stewart's double. Soriano followed with his blast, which appeared to clear the scoreboard in left field.
Todd Frazier led off the Reds' second with his third spring home run, connecting on the first pitch from Paul Maholm, who was making his first Cactus League appearance. The left-hander departed after giving up one run on two hits over two innings.
Chicago loaded the bases in the second and made it, 4-1, on Byrd's sacrifice fly. Arroyo gave up four runs on six hits and two walks over two innings in his second Cactus League start.
The Reds closed to, 4-3, in the third on Zack Cozart's two-run double off Jeff Samardzija. Samardzija had given up one hit over three scoreless innings in his first Cactus League appearance, and was charged with two runs on two hits in three innings. He retired the last eight batters he faced in order.
Cubs closer Carlos Marmol continued to struggle. He came on in the seventh and walked the first batter, then served up a double to Ryan Ludwick. One out later, Marmol hit Corky Miller with a pitch and Donald Lutz followed with a two-run single to left.
Mather, contending for a spot on the bench, connected off Carlos Fisher with two outs in the Chicago seventh to give the Cubs a 7-6 lead.
Up next: The Reds will travel to Surprise, Ariz., on Tuesday to face the Royals at 4:05 p.m. ET. Mike Leake is scheduled to start and pitch in his third spring game. The right-hander has given up seven hits over four innings so far. Also scheduled to pitch are Sam LeCure, Sean Gallagher and Nick Christiani.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter@CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.