The Cubs have lost 100 games only twice in team history, 1962 and '66, when they finished 59-103 both times.
"Tomorrow is as important as any game we play," Cubs manager Dale Sveum said.
Justin Upton drove in three runs, including two on his 17th home run, to back Trevor Cahill's complete game four-hitter and lift the D-backs to victory.
The Cubs also need a win on Sunday to avoid becoming the first Major League team to go winless against one division on the road in a single season. Chicago is 0-18 on the road against the National League West: San Francisco (0-4), Arizona (0-5), Los Angeles (0-3), San Diego (0-3) and Colorado (0-3).
It isn't just the Pacific or Mountain Time Zones that are a problem, either. The Cubs have lost a franchise-record 58 games on the road.
"Our road record has been pretty awful," Sveum said. "Not very good teams, that's usually what happens. You don't want to lose this many games. ... You wish you had the magic potion for that one. Even great teams struggle on the road. You don't want to struggle this bad. That's one thing going into next year, you have to get better at."
Soriano did his part, although it came late when he hit a two-run home run in the ninth, his 32nd. He is the first player in franchise history to reach 108 RBIs at the age of 36 or older.
"I know I'm 36 years old, but I don't feel like it," he said. "My body feels good, my hands. I know my knee is not the same, but my hitting, my hands are still the same."
"I was 0-2 [in the count] and trying to throw one off the plate so he would ground out, get a double play and end it, but it stayed up high," Cahill said. "He's a good player."
Despite the blast, the Cubs have been outscored, 80-53, this month away from Wrigley Field.
"You're basically just overmatched," Sveum said. "You can't sugarcoat it or anything like that."
Justin Germano (2-10), making his last start of the season, gave up seven runs over 4 1/3 innings, and heads home Sunday to be with his wife, who is expecting the couple's second child. The right-hander admitted he "hit the wall" in the last month.
"He's done as best as he can, but it's tough to go out there against lineups with five, six left-handed hitters and try to get away with 86 mph," Sveum said. "I feel bad for him, because he's done everything we've asked. He's gone out there every time. I appreciate that."
The D-backs sent eight batters to the plate in the first and opened a 3-0 lead on an RBI double by Aaron Hill and RBI singles by Upton and Mike Jacobs. In the Cubs' five games on this road trip to Denver and Phoenix, they've been outscored 9-3 in the first inning, and have scored first once, and that was on Tuesday against the Rockies.
Hill added an RBI single in the second. Germano's first four pitches in the fifth resulted in a groundout, single, home run by Upton, and hit batter.
"I felt the curveball to Upton was the worst pitch I threw all night," Germano said. "I watched it on video, and I don't know how he hit it out, it was that bad of a pitch."
Upton, who had admired his home run, wasn't happy Miguel Montero was plunked, and yelled at Germano from the dugout. The right-hander didn't hear him.
"It wasn't on purpose that I hit Montero," Germano said. "I even made eye contact with Montero and he knew. I think everyone else in the stadium thought it was. It was bad timing. ... I think [Upton] was yelling, 'Hit me, hit me,' or something like that. That's not my game. I give up home runs all the time. If I hit people after, I'd be hitting quite a few people."
Actually, he has. Germano has given up seven home runs with the Cubs, and hit seven batters.
Cahill (13-12) also hit an RBI single with two outs in the seventh, one of 15 hits by the D-backs. The Cubs have served up double-digit hits in their last seven games.
Soriano said he won't say anything to the players before Sunday's game.
"They know," he said. "They're a part of this. They don't want to be a part of a team that loses 100 games. If it happens, that can give them motivation to next year. I know we have a losing season, but, so far, we're having fun. We try our best all the time and play nine innings."