The three RBIs gave Williams 100 for the fourth time in his career. He ranks second in the majors to Mark McGwire's 102 RBIs.
"Matt is so consistent, he's had so many opportunities with runners in scoring position and two out and he's come through," teammate Jay Bell said. "You hear stuff about the MVP and (games like Monday) have to be weighed into that. We wouldn't be in the position we are without him."
Said Arizona manager Buck Showalter: "Matt's been as steady as you can be. He's a special man. I'm biased, but it's been a pleasure watching him play every day."
Sosa pulled within one of McGwire, who also leads the majors in homers. Sosa had been in a 1-for-22 slump since last connecting on Aug. 4.
Chicago's Mark Grace said the team's current slump is more humiliating than the 0-14 start in 1997.
"This is worse," Grace said. "We weren't a very good team (in 1997). This team has a lot of talent."
"Anything that can go wrong has gone wrong," said Cubs manager Jim Riggleman, who talked to the team after the loss. "We've got seven weeks left to show we've got some pride."
Omar Daal (11-6) won for the eighth time in his last 10 decisions, giving up two runs and four hits in seven innings.
After Sanders walked Erubiel Durazo to load the bases, reliever Felix Heredia retired Steve Finley on a popup. Bernard Gilkey hit a grounder to third baseman Jeff Blauser, who threw the ball into the outfield for an error, allowing two runs to score.
"By the time Blauser got the ball, it was wet," said Riggleman, partially blaming a steady drizzle for the miscue. "It was sinking and tough to handle."
Benito Santiago hit a three-run homer in the Cubs ninth.
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