Ben Gamel led off the eighth with a double against Nick Turley (0-1) and scored on Arcia's hit off Chris Stratton as the Brewers took three of four in the series.
''I was looking for something off speed,'' Arcia said through a translator. ''I was just trying to put the ball in play. He left one up and I was able to connect on it.''
Pirates manager Derek Shelton wasn't thrilled with the location of the pitch to Arcia.
''It wasn't the pitch selection, it was the execution of the pitch,'' he said. ''When you see the execution of two-strike pitches from really good pitchers, they don't do too much with it, and they end up getting the swing and miss or weak contact.''
Josh Hader pitched a perfect ninth for his eighth save in his first appearance since walking five of the six batters he faced while trying to close out Saturday night's game. Hader has yet to give up a hit this season.
''I really didn't have much concern,'' Brewers manager Craig Counsell said. ''Josh is going to have a bad night. That's alright. That's how it works. He's a great pitcher and that's what they do. They come back out the next time and get it done.''
Devin Williams (3-1), the fourth of five Brewers pitchers, struck out four and didn't allow a hit in 1 1/3 innings to pick up the win.
Keston Hiura homered for the Brewers, who also took advantage of shoddy fielding by the Pirates.
The Brewers got two runs in the second when Pittsburgh second baseman Kevin Newman bobbled Eric Sogard's grounder with the bases loaded. Sogard was awarded a hit and an RBI, with the second run crossing on Newman's throwing error to first.
Pittsburgh tied it in the third on Erik Gonzalez's two-out, two-run homer off Brent Suter, who retired eight straight to start the game before walking Cole Tucker.
The Brewers took advantage of another error by Newman in the fourth that allowed struggling Omar Narvaez to score after his leadoff double.
Milwaukee extended its lead to 5-3 in the fifth on Hiura's leadoff homer that chased starter Trevor Williams. Hiura has four home runs in 10 games against the Pirates this season and 10 in 26 career games versus Pittsburgh.
''He can spoil some really good pitches,'' Williams said.
Williams gave up seven hits and five runs (three earned) in four innings.
The Pirates tied it again in the sixth on Jose Osuna's two-run single off reliever Freddy Peralta.
Pirates: Reinstated 3B Colin Moran from the seven-day concussion injured list and optioned 1B Will Craig back to their alternate training site in Altoona, Pennsylvania.
Brewers: OF Avisail Garcia was out of the starting lineup for the third consecutive game due to ankle soreness. He pinch-hit in the eighth. ... OF/DH Ryan Braun sat out with back soreness. . Placed RHP Brandon Woodruff on the paternity list. . Sent RHP Corey Knebel (strained hamstring) to the alternate training site in Appleton, Wisconsin, on a rehab assignment. . Recalled RHP Trey Supak and RHP Justin Topa from the alternate training site.
The Brewers traded reliever David Phelps to the Phillies for three lower-level prospects to be named later. Phelps, 33, was in his first season with Milwaukee after signing as a free agent on Jan. 30. He appeared in 12 games and had a 2.77 ERA in 13 innings. ''It became very clear early on that David was an attractive player to a number of teams,'' Brewers general manager David Stearns said.
The Brewers tried to swing a deal for a hitter to add to the team's offense-starved lineup right up until Monday's 3 p.m. CDT trade deadline. ''Up until probably about 2:55, I thought we were going to add a bat,'' Stearns said. ''I thought we were close. Sometimes it doesn't work.''
The Pirates, in a rebuild under first-year general manager Ben Cherington, opted to stand pat at the trade deadline, save for sending veteran center fielder Jarrod Dyson to the Chicago White Sox last week for international signing money. With closer Keone Kela injured and most of Pittsburgh's hitters struggling, the Pirates didn't have much leverage and Cherington said the club was focused on procuring ''long-term'' returns.
SAY HEY TO HAYES
The future appears to be now for Pirates third base prospect Ke'Bryan Hayes. A three-time Gold Glove winner in the minors, Hayes is expected to be called up from the team's alternate training sight in Altoona on Tuesday and could make his major league debut when Pittsburgh opens a three-game series with the Chicago Cubs. Hayes' father, longtime major league third baseman Charlie Hayes, tweeted Monday that his son had made it to The Show.
Pirates: Chad Kuhl (1-1, 2.52 ERA) will take the mound Tuesday against the Chicago Cubs as Pittsburgh begins a nine-game homestand. Kuhl is 1-6 with a 6.75 ERA in nine career starts against the Cubs.
Brewers: Josh Lindblom (1-2, 6.31) gets the start in the opener of a two-game interleague series against the Tigers at Miller Park. Michael Fullmer (0-0, 8.79) goes for Detroit.
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