Frankie Montas (2-1) pitched seven shutout innings, allowing two hits without walking a batter and striking out five for the AL West-leading A’s.
The three-time reigning division champion Astros lost their fourth in a row. The last three defeats had been by a total of four runs.
Semien became the first player in A’s franchise history with a game-ending hit and a leadoff homer on back-to-back days.
Matt Chapman homered in the eighth and added an RBI groundout in the sixth as Oakland (11-4) matched the 2014 club for the best record through 15 games over the last 30 years.
Houston starter Framber Valdéz (0-2) gave up two runs and seven hits, striking out nine with one walk over seven innings.
YANKEES 8, RAYS 4, 1st game
ST. PETERSBURG, Fla. — Gerrit Cole came within one strike of earning his 20th straight regular-season win before getting pulled, and New York won the opener of a seven-inning doubleheader.
Cole took a 5-0 lead into the fifth. With two outs and a runner on, he had a 1-2 count on Ji-Man Choi, who came back to hit an RBI double. Jose Martinez followed with a two-run homer on the 107th pitch from a clearly tiring Cole. Soon after, Yankees manager Aaron Boone took a slow walk to mound to replace Cole with Chad Green (2-0), who got the win after allowing one run over 1 1/3 innings.
Cole struck out 10, walked one and gave up six hits.
Aaron Judge hit his eighth home run of the season for the Yankees. Giancarlo Stanton and Mike Ford also connected for New York.
After Ford homered, a two-run double by Gio Urshela put the Yankees up 4-0 and chased Rays starter Tyler Glasnow (0-1) with two outs in the third.
TIGERS 11, PIRATES 5
PITTSBURGH — Niko Goodrum, Miguel Cabrera, C.J. Cron and Jeimer Candelario all hit home runs in the first inning against Pittsburgh’s Derek Holland to lead Detroit.
Detroit sent four of Holland’s first 11 pitches over the fence at PNC Park to propel the Tigers to another big offensive outburst against reeling Pittsburgh one night after a 17-13 win in 11 innings.
The Pirates lost for the ninth time in their last 10 games.
Cabrera got three hits, including his 481st career home run. The 37-year-old also drove in three runs.
Ivan Nova (1-0) nearly let a big early lead slip away. The veteran gave up five runs on six hits with three walks and three strikeouts.
Kevin Newman tied a career-high with four hits and drove in two runs for Pittsburgh.
INDIANS 7, WHITE SOX 1
CHICAGO — Zach Plesac tossed six strong innings and Cleveland snapped a scoring drought with a six-run fourth.
The Indians had been blanked for 13 innings before Franmil Reyes and Jordan Luplow each hit a two-run homer in the fourth. Luplow was 0 for 21 with a walk this season before homering. Domingo Santana added a solo homer in the eighth.
Plesac (1-1) allowed five hits and struck out seven in lowering his ERA to 1.29 this year.
Yoan Moncada homered in the eighth for Chicago. He has reached in 19 straight games dating back to last Sept. 25.
The Indians were held hitless through the first three innings before erupting against Drew Anderson (0-1) in the fourth.