When Bubba Chandler made his major league debut out of the bullpen, it begged a question: Why wasn’t the game’s top pitching prospect starting games instead of coming on in relief?

Chandler’s first MLB start answered that.

Facing the team with the best record in baseball — and going opposite the Steelers’ season opener — Chandler got rocked for nine runs on nine hits and three walks in 2 2/3 innings as the Milwaukee Brewers barreled their way to a 10-2 win Sunday afternoon before 12,443 at PNC Park.

The NL Central-leading Brewers (89-55) had 14 hits and seven walks to complete a three-game series sweep of the Pirates (64-80), who began the six-game homestand with a three-game sweep of the NL West-leading Los Angeles Dodgers but ended it with a resounding thud.

It was the 10th time this season an opponent scored double-digit runs against the Pirates and the third time the Brewers have done so. They beat the Pirates by scores of 14-0 and 12-5 on Aug. 12-13 at American Family Field in Milwaukee.

Chandler also faced a tall order in his counterpart, Brewers 6-foot-7 rookie right-hander Jacob Misiorowski (5-2). The 23-year-old All-Star had eight strikeouts allowed one run on three hits and two walks. He threw his fastball on 60 of his 108 pitches, averaging 99 mph and topping 100 11 times with a maximum of 101.2.

Through his first three outings, the 22-year-old Chandler had shown why he was such a highly regarded prospect. His fastball flirted with triple digits, and his changeup proved to be a strong secondary pitch. He earned a scoreless four-inning save in his debut and the win in each of his next two appearances, allowing a total of three runs on nine hits and one walk with nine strikeouts in a combined 12 innings.

Against the Brewers, Chandler showed why the Pirates were slow to pull the trigger on his promotion and left him to spend much of the summer at Triple-A Indianapolis. He gave up hits to four of the first five batters he faced and walked the other. Of the 19 batters he faced, 14 reached base. Chandler threw 43 of his 68 pitches for strikes, recording three strikeouts, but got only one whiff on 15 swings against his fastball.

Chandler (2-1) got off to a rocky start when Brice Turang hit his second pitch for a single through short, and Isaac Collins followed with a single to left. After Chandler got ahead in the count against William Contreras, he threw four consecutive balls for a walk to load the bases.

Jake Bauers doubled down the right-field line to drive in two runs, and Andrew Vaughn hit a flare to right for an RBI single and 4-0 lead. Chandler got Caleb Durbin to ground into a 4-6-3 double play and Blake Perkins to fly out to center to end the frame.

Danny Jansen led off the second with a double to right, advanced to third on a Joey Ortiz single and scored on a wild pitch by Chandler to give the Brewers a 5-0 lead.

The Pirates pushed across a run in the bottom of the second, when Andrew McCutchen hit a leadoff double and scored on a Liover Peguero single that dropped in left to cut it to 5-1.

But Chandler gave up four more runs in the third: on an RBI double by Blake Perkins, a fielder’s choice to score Vaughn from third and a two-run single by Turang for a 9-1 Brewers lead. That was it for Chandler, who was replaced by Colin Holderman with two outs.

Misiorowski struck out the side in the fourth by getting McCutchen swinging at a 98.4-mph fastball, Oneil Cruz looking at a curveball and blew a 101.2-mph heater by Joey Bart for a called third strike to end the inning. Misiorowski retired the final 13 batters he faced.

The Brewers padded their lead against Yohan Ramirez in the seventh, when Bauers hit a leadoff single and scored on a bases-loaded groundout to third by Jansen to make it 10-1.

The Pirates finally scored again when Joel Payamps replaced Misiorowski in the eighth. Ji Hwan Bae, recalled from Indianapolis on Sunday, drew a one-out walk and had a chance to show off his speed by scoring from first on pinch hitter Cam Devanney’s double to left.