The Brewers pulled that one out after a 6-5 victory in which they lost starter Gallardo to a tight left hamstring.
That was the biggest news of the day, particularly with the non-waiver deadline approaching on Wednesday and the pitcher's name circulating in trade rumors.
Now, his status is up in the air and manager Ron Roenicke said the team will know more after Gallardo is examined by team physician Dr. William Raasch on Wednesday.
"We're not sure as far as length of time," Roenicke said.
In the second game, they got six scoreless innings from Tyler Thornburg and a leadoff homer from Juan Francisco in the fifth. Bianchi got a bit of redemption after he booted a grounder to short by Cole Gillespie in the seventh -- one of two errors in the inning by Milwaukee that led to a two-run double by David DeJesus off Burke Badenhop.
"That's what's great about this game," Bianchi said. "You get a chance in the (top) of the ninth to redeem myself a little bit for the mistakes early on in the game.
Chicago took a 2-1 lead to the ninth, but closer Kevin Gregg (2-3) couldn't hold it.
Then, Castro decided to dive for Bianchi's soft liner to deep short when he might not have needed to, and the ball fell out of his glove, allowing two runs to score.
DeJesus made a lunging catch in deep center to rob Jonathan Lucroy and end the rally.
Castro said the ball wasn't hit quite as hard as he thought. Even so, he insisted he made the right call by diving.
"I was running hard," he said. "I can't stop. I stretched it out the best I can."
Bianchi's hit made a winner of Badenhop (2-3), who gave up two unearned runs in two innings.
Jim Henderson worked the ninth for his 14th save in 17 chances and second of the day. He also survived a wild ninth in the opener.
In his first start this season and seventh appearance, Thornburg allowed just four hits and struck out six while walking three. And he could wind up in the rotation if the Brewers have to go without Gallardo.
"After that ballgame it would be a nice little fit. We'll see what happens with Yo and we'll make that decision," Roenicke said.
In the opener, Segura hit a solo homer and the go-ahead double, Khris Davis added a three-run shot, and the Brewers rallied to beat Chicago after Gallardo hobbled off the field in the fifth.
Davis' homer in the seventh on the first pitch from reliever James Russell (1-3) wiped out a 5-2 deficit, and Segura capped the four-run rally with an RBI double, giving the Brewers a 6-5 lead.
Milwaukee survived a major scare after Henderson came on in the ninth.
Pinch-hitter Dioner Navarro walked with two out and Welington Castillo barely missed a winning homer, driving a 2-0 pitch just foul beyond the left-field wall. He wound up walking before pinch-hitter Cody Ransom flied to center, giving Henderson 13 saves in 16 chances.
Segura and Betancourt hit solo homers as Milwaukee built a 2-0 lead, but that unraveled in the fifth.
The Cubs tied season highs with five runs and six hits in the inning. Gallardo came up clutching his leg after delivering a 1-2 pitch to Darwin Barney with two out and the bases loaded and immediately left the game.
Gallardo allowed three runs and six hits. He first felt pain in the hamstring in the fourth, when he made a diving catch on Villanueva's bunt.
"As soon as I released it, it kind of tightened up a little bit," Gallardo said. "After I felt it on that pitch I figured it was going to be a little difficult to stay in there."
Villanueva, who gave up six hits and four runs in 6 1/3 innings for Chicago, was in line for the win after dropping his previous three starts before the Brewers rallied against Russell.
Although Jeff Samardzija's name has surfaced in trade rumors, Cubs manager Dale Sveum said he thinks it's "very, very far-fetched" that he gets dealt before Wednesday's deadline. Samardzija, 6-9 with a 3.75 ERA, is not scheduled to become a free agent until after 2015. ... RHP Scott Baker (Tommy John surgery) continued to struggle in his fourth minor league rehab start on Monday, giving up three hits and two runs in 3 1/3 innings for Class A Daytona. ... Roenicke said he didn't expect any deals before the deadline. ... Marco Estrada threw 2 2/3 innings Monday for Milwaukee's Arizona Rookie League team in his first appearance rehabbing from a strained left hamstring suffered June 3. Roenicke said Estrada will pitch Friday, although the location hasn't been determined, and that he'll need a minimum of two more starts before returning. ... RHP Edwin Jackson (6-11, 4.89 ERA) starts Wednesday for the Cubs, and RHP Wily Peralta (7-10, 4.54) pitches for Milwaukee.