Dansby Swanson scored the tiebreaking run standing up on an infield grounder to spark a four-run sixth inning, and the Chicago Cubs reached Oakland's bullpen for 10 runs in a 12-2 victory over the Athletics on Wednesday that completed a three-game sweep.

The A's have lost seven straight and at 3-16 are mired in their poorest 19-game start since the 1951 Philadelphia A’s.

Eric Hosmer hit his first home run since last July 29 for San Diego, Patrick Wisdom had a two-run triple and Nico Hoerner added three hits for the Cubs. Luis Torrens drove in two runs with a bases-loaded double in the ninth.

Justin Steele (3-0) struck out five in six innings, allowing two runs - one earned - and four hits. The left-hander, who won four games in 24 starts last season, has given up two earned runs or fewer in 11 consecutive starts dating to last year.

Mason Miller, a 24-year-old right-hander who is Oakland’s top pitching prospect, made his major league debut and allowed two runs, four hits and one walk with five strikeouts in 4 1/3 innings. The 6-foot-5 right-hander, a third-round pick in the 2021 draft, reached 100 mph with 15 of 81 pitches and averaged 99.3 mph with 53 fastballs.

He retired nine of his first 10 Chicago hitters before the Cubs scored single runs in the fourth and fifth.

With the score 2-2, Swanson and Ian Happ drew back-to-back walks off Chad Smith (1-1) to begin the sixth. After both runners moved up on a wild pitch, Cody Bellinger hit a sharp grounder to first baseman Jesús Aguilar off Sam Moll. Aguilar attempted to get the out at home, but Swanson beat the throw standing up.

After Torrens struck out swinging, Wisdom tripled for a 6-2 lead.

Hosmer homered off Adam Oller in the eighth.

Keegan Thompson and Julian Mayweather combined to get the final nine outs for the Cubs.

Carlos Pérez and Jordan Diaz had RBI doubles for Oakland.

Jameson Taillon (0-2, 7.00 ERA) starts Friday in Los Angeles seeking his first career win in five outings against the Dodgers.