The Rangers have won the first game of a series three straight times but have still failed to win a series since June.
However, they trailed 5-0 in the second inning en route to a 9-3 loss to the Athletics. Texas has lost 15 of its last 18 and dropped to 4-19 in July.
Oakland's John Jaso drove in three runs, helping Scott Kazmir to his 12th win — tied for the American League lead.
"Tonight, it was just the pitching," Texas manager Ron Washington said. "We couldn't muster anything."
The Rangers' own pitching, clutch hitting and fielding, weren't very good either.
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Miles Mikolas (1-3) allowed seven earned runs on seven hits and four walks in 4 2-3 innings. He was coming off his first major league win as a starter, over the Yankees July 21.
"I fell into some of the bad habits that we'd been working on in the bullpen," Mikolas said. "I executed well and made the transition well in the New York game, and kind of fell back. I'm going to work on it."
With one out, he walked Jed Lowrie and Eric Sogard. Craig Gentry, the No. 9 hitter, hit a soft grounder to Mikolas, who threw to second hoping to start a double play but the ball went into center field. Lowrie scored on the play.
Jaso and Vogt followed with run-scoring hits. Cespedes doubled to drive in the final two runs.
In the third and fifth innings, Rangers No. 5 batter J.P. Arencibia went to the plate with a total of five runners on base. Kazmir struck him out both times.
Jaso had added a two-run double in the fifth, when Oakland extended the lead to 8-2.
The Athletics' first three batters — Jaso, Stephen Vogt and Yoenis Cespedes — each had a double and a single, and Josh Reddick added three singles.
Kazmir (12-3) allowed seven hits in five innings. He walked two and struck out two.
Athletics manager Bob Melvin said: "It was maybe not his best command at times. But seeing him be so good this season, that five-inning outing doesn't look so good."
The victory enabled Oakland to remain two games ahead of the second-place Los Angeles Angels in the AL West. The Athletics are 7-5 against the Rangers this season.
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Adam Rosales had a two-run homer in the second for the Rangers that cut their deficit to 5-2.
Adrian Beltre added a solo shot off reliever Evan Scribner in the eighth. Beltre was 2 for 3 with a double and a walk.
Jaso has an 11-game hitting streak against Texas and a 15-game streak as the Athletics' leadoff batter. He is batting .394 (13 for 33) against the Rangers this season.
