Gorzelanny (4-1) scattered one run and three hits in his 7 1/3 innings of work, striking out six Reds batters and walking one. Of his 98 pitches, 66 were strikes.
He opened the game with seven scoreless innings and left to a standing ovation from Cubs fans, who not unusually made up the majority of the 17,992 in attendance.
"It shows how big this team is, having more fans here than the home team," Gorzelanny told reporters after the game.
Those fans got their money's worth.
After allowing a one-out triple to Reds third baseman Adam Rosales in the first, Gorzelanny proceeded to strike out the next two batters he saw to get out of the inning unharmed. He retired seven in a row and 13 of 14 batters.
Gorzelanny left in favor of lefty setup man Sean Marshall in the eighth after allowing a Willy Taveres single with one out that put two runners on. Marshall and right-hander Angel Guzman combined to get the Cubs out of the inning with a 6-1 lead.
"What a nice game Gorzelanny pitched," Cubs manager Lou Piniella said. "A great way to break in here."
Gorzelanny also helped his cause with the bat, driving in Alfonso Soriano as part of a four-run sixth inning that chased Reds starter Johnny Cueto (8-9) and staked Chicago to a 5-0 lead.
Gorzelanny and left-hander John Grabow were acquired from Pittsburgh last week for RHP Kevin Hart and two minor leaguers. He spent much of this season in the minor leagues at Class AAA Indianapolis, making 15 starts with a 2.48 ERA.
Cubs scouts who saw Gorzelanny at Indianapolis turned in favorable reports on the southpaw, a 14-game winner with Pittsburgh two seasons ago.
"Our reports on Gorzelanny were outstanding," Cubs Assistant General Manager Randy Bush said Tuesday. "We had four or five different scouts see him this year. He was a guy that we thought might be available and all of our reports were excellent.
"Dave Littlefield had a real good history with him from his time with the Pirates, and he went and saw him about a week to 10 days before we actually made the deal and turned in another favorable report."
Kosuke Fukudome and Derrek Lee each hit solo home runs and the Cubs (57-48), mired by injuries and inconsistency throughout the first half, improved to 14-5 since the All-Star break — the best mark in the National League.
The Cubs are tied with St. Louis for first place in the National League Central, helped in part by Chicago's five wins over the Reds in the second half.
For Gorzelanny's part, he'll hold down a spot in the rotation at least until left-hander Ted Lilly (shoulder, knee) returns from the disabled list later this month.
"We were happy to get him," Bush said of Gorzelanny. "He's a left-hander that has had success in the big leagues. He won 14 games in 2007. We hope he can get back to pitching with that kind of success in the big leagues.
"Obviously we're hopeful that Ted Lilly will be back sooner rather than later, but we also know that it's the nature of the game that you better have enough starting pitching because somebody else is liable to get nicked up along the way."
Gorzelanny Shines in Cubs Debut
Northsiders Report Top Stories
Cubs Oct. 21 NotebookCubs moved closer to the World Series and a light night of action for Cubs prospects in the winter leagues.
Northsiders Report3:02 PM
VWL opens play, 7 Cubs in leagueThe Venezuelan Winter League has started its season and several Cubs prospects are playing, including LHP Gerardo Concepcion.
Eugene recapEms not only had the best winning percentage of any stateside minor league team, they captured the NWL crown
AZL Cubs RecapIsaac Paredes, Gustavo Polanco and Eugenio Palma all earned post-season honors while the Cubs reached the post-season.
Cubs 1 DSL recapJonathan Sierra, Yonathan Perlaza and Brailyn Marquez highlighted the Cubs 1 roster