Russell (5-1) began the eighth after Wood held the Reds to only one run in seven innings, but promptly gave up a leadoff double to Drew Stubbs. Brandon Phillips followed with a single before Ludwick pulled Russell's 2-2 offering into left field to score both.
Despite Ludwick getting doubled off moments later on Todd Frazier's flyout to left fielder Alfonso Soriano, the Reds added an insurance run when Chris Heisey doubled, stole third and came home on Wilson Valdez's single.
"I'm kind of [ticked] that it ended up that way, but I executed some good pitches and, unfortunately, sometimes good pitches get hit and they find holes," Russell said.
Wood hit for himself in the bottom of the seventh before being replaced by Russell. Cubs manager Dale Sveum said he batted Wood -- a .200 hitter this season -- to save the bench because he knew he was going to put Joe Mather in right field as a defensive substitution.
Wood was removed after throwing 99 pitches, but has topped the century mark only four times, with his season high at 104.
"Russell had some rest and [he and right-hander Shawn Camp] have been our guys in the later innings," Sveum said. "Unfortunately, some bloopers and seeing-eye ground balls found the way."
Unlike Chicago's bullpen, Cincinnati's was able to preserve its starter's solid outing.
Reds right-hander Bronson Arroyo (8-7 3.95 ERA) allowed a two-out, two-run single by David DeJesus in the second inning, but that was it, allowing only one other baserunner -- a sixth-inning single by Starlin Castro. He retired 19 of the final 20 batters he faced before closer Aroldis Chapman earned his 27th save in the ninth.
Arroyo improved to 5-0 with a 2.53 ERA in his last seven starts at Wrigley Field.
"[Wood] was making good pitches and Bronson made good pitches, too," Ludwick said. "I thought both of the offenses had a tough time today with some good pitching. We were fortunate to have that one inning where they brought in someone new."
Although the no-decision snapped Wood's career-high five-game losing streak, Cincinnati's comeback kept him from earning his first victory since July 6. It also cost him an opportunity for revenge on the Reds, the team that drafted him in the second round in 2005, developed him and had him in their starting rotation the past two seasons before trading him this offseason.
Wood put on an impressive performance, tying a career high by striking out eight and allowing only five hits.
"Probably be lying if I said there wasn't," Wood said of feeling extra motivation. "First time facing them since leaving them, and it was exciting."
Cincinnati scored its first run in the fourth, when Phillips led off with a double and scored on Frazier's single -- the only inning Wood allowed more than one runner on base.
"He pitched as good as you possible could against all nine guys in the lineup," Sveum said. "That was as impressive an outing as he's had all year."
Despite having a 4.52 ERA on the season and spending a couple of stretches in the Minors, Wood has been solid for the Cubs. He has given up three-or-fewer runs in 12 of his 16 starts this season, including allowing just three in his last three starts.
"As a whole, yes," said Wood, 25, when asked if he's been pleased with his season. "I've progressed, I've had some good games, had some bad games, but that's baseball. The bad games you've got to learn from and do everything you can out there to help your team win."
Wood put the Cubs in position to do that Saturday, but Arroyo was equally as good. The right-hander also allowed more than one runner to reach base in an inning only once, in the Cubs' two-run second.
Third baseman Luis Valbuena doubled, Bryan LaHair walked and Steve Clevenger singled -- all with one out -- to bring up Wood in the bottom of the second. Wood struck out swinging, but DeJesus knocked Arroyo's 0-2 pitch up the middle to bring in what would be the Cubs' only two runs.