Freddy Peralta (2-0) struck out 10 over six innings of two-hit ball for the victory. Milwaukee has won five of six, while the Cubs lost for the fifth time in six games.
After being shut out on one hit by Chicago starter Adbert Alzolay (0-2) through five innings, the Brewers loaded the bases to start the sixth. After the Cubs cut down a runner at the plate, Alzolay, who had retired 11 straight coming into the inning, gave way to reliever Andrew Chafin.
Urias, who entered 2 for 27 on the season, batted for Daniel Vogelbach and slapped a shot just inside the left-field line to clear the bases.
''You never know when you are going to get the opportunity to get into the game,'' Urias said. ''I was lucky to get the opportunity my teammates made for me. I was ready.''
It was Urias' first career pinch hit in six at-bats.
''It was a huge spot in the game,'' Brewers manager Craig Counsell said. ''Contact helps us there even to tie the game and he jumped on a first-pitch slider and did something good with it.''
Urias later scored on a wild pitch to grow the lead to 4-1. Jackie Bradley Jr. knocked in another run with a triple and Keston Hiura added an RBI single as the Brewers sent 11 batters to the plate in the inning.
Peralta gave up just one run, a fourth-inning homer by Kris Bryant. The right-hander walked two and reached double digits in strikeouts for the fourth time in his career, the last coming in April 2019.
Peralta got aggressive and retired the next nine batters, including six strikeouts, after Bryant's home run.
''I was so focused on that pitch and I don't know how he hit it that great,'' Peralta said. ''I got mad after that one.''
Josh Hader got two outs for his first save of the season. Hader came on after Javier Baez drove in a pair of runs with a one-out double.
The Cubs announced before the game that bullpen coach Chris Young tested positive for COVID-19. First base coach Craig Driver already was away from the team following a positive test. Relief pitchers Brandon Workman, Jason Adam and Dan Winkler were placed on the COVID-19 injured list. There was no word on whether their designation was the result of a positive test or contact tracing.
The Cubs have had five hits or fewer in seven of their first 10 games.
''It feels like we're very homer-dependent right now,'' manager David Ross said. ''This is too talented of a group to do what we're doing so far. We've got to climb out of that.''
Alzolay gave up five runs and three hits in 5 1/3 innings. He struck out six and walked one.
Chafin allowed three runs while getting just one out. He threw a wild pitch and hit a batter.
The Brewers called on Angel Perdomo to pitch the ninth inning but after umpires intervened, the left-handed reliever was forced to leave the mound. Turns out Perdomo, who had just been recalled from the team's alternate training site, wasn't on the official lineup card.
''It's our mistake. It's an automated system now when you make a roster move, but it's our responsibility to check the lineup,'' Counsell said. ''For whatever reason, he wasn't on the lineup card given to the umpires. We were taught a lesson tonight.''
Cubs: To fill the roster spots of Workman, Adam and Winkler, the club recalled left-handers Justin Steele and Brad Wieck from the team's alternate training site in South Bend, Indiana, while veteran reliever Pedro Strop was selected as a replacement player from the alternate site. Steele and Wieck both appeared in relief.
Brewers: OF Christian Yelich sat out after leaving Sunday's game with back soreness. ''We're still in a day-to-day situation,'' Counsell said. Bradley started in left field, replacing Yelich, for the first time since 2015. .3B Travis Shaw, who also exited Sunday's game after fouling a pitch off his shin, returned to action.
Cubs: RHP Kyle Hendricks (0-1, 3.00 ERA) tossed six scoreless innings against the Brewers last Wednesday, allowing four hits and one walk with six strikeouts. Hendricks in 9-6 with a 2.72 ERA in 25 career starts against Milwaukee.
Brewers: RHP Brandon Woodruff (0-0, 2.45) gave up one hit in seven shutout innings at Chicago on Wednesday. Opponents are batting .179 (7 for 39) against Woodruff this season.
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