ARLINGTON, Texas — The best team in the American League West beat up on the Mariners’ best pitcher in 2016 with frightening ease. And the Rangers’ dominance over Seattle continued Monday at Globe Life Park.

Texas scored five runs and knocked Hisashi Iwakuma out of the game after three innings in a relatively easy 6-3 victory over the Mariners.

Iwakuma suffered through his third consecutive defeat while his team has lost three in a row and six of its past seven games. Seattle is 4-9 against the Rangers this season.

The Mariners continued to plummet in the American League wild-card race. With the defeat, Seattle falls to 68-63 — four games back. Meanwhile, the Astros and Royals, who both won Monday night, moved to 69-62 — a game up on Seattle.

The expected pitchers’ duel between Iwakuma and fellow countryman Yu Darvish never really developed. Darvish toyed with Mariners hitters for the first six innings before his pitch count forced him from the game. He improved to 5-3 on the season.

It was a shirt-soaking, hit-enduring battle for Iwakuma. After two quick outs in the first inning, Iwakuma made a mistake to the slumping Carlos Beltran. Iwakuma hung a slider over the middle of the plate that Beltran blasted into the upper deck in right field for solo homer. Beltran was just 2 for 34 coming into the game, but was 4 for 9 against Iwakuma in his career.

Iwakuma worked a scoreless second inning, but the third would be his undoing. The Rangers scored three runs on four consecutive hits:

• Leadoff single of Elvis Andrus.

• Run-scoring triple to right field from Nomar Mazara.

• Line-drive double to the wall in left field from Ian Desmond.

• A run-scoring double from Beltran over the head of Leonys Martin in center.

• Two outs later, Jonathan Lucroy dumped a single into left to score another run and make it 5-0.

When Iwakuma finally struck out Carlos Gomez, after an 11-pitch at-bat, it was his 40th pitch of the inning and 68th in three innings. There was no reason to bring him out for another inning of getting knocked around when he obviously didn’t have the command or life on his pitches to get outs.

His line: three innings, five runs allowed on six hits with a walk and two strikeouts to fall to 14-10.

Seattle ensured it wouldn’t be shutout by Darvish in the fourth inning after the Rangers took the big lead. Kyle Seager drew a two-out walk and scored from first base on Adam Lind’s double to the gap in right-center to make it 5-1.

The Rangers tacked on an insurance run in the second of three innings worked by switch-pitcher Pat Venditte, who replaced Iwakuma to start the fourth. Adrian Beltre doubled with one out in the fifth, moved to third on a passed ball by Mike Zunino and scored on a sacrifice fly to center from Rougned Odor to make it 6-1.

Venditte’s outing still was considered a positive. He worked three innings, allowing just the one unearned run on one hit with a walk and five strikeouts.

Seattle picked up two more runs in the seventh, forcing Darvish out of the game and had the chance to make it very interesting in the final innings.

With Shawn O’Malley on first base, Martin’s single to center ended Darvish’s night. Rangers manager Jeff Bannister called on lefty Jake Diekman. The Mariners countered with pinch-hitter Franklin Gutierrez. The veteran right-handed hitter delivered, doubling down the left-field line past a diving Beltre to score both runners.

Down 6-3, Diekman walked Robinson Cano on four pitches to bring the tying run to the plate in Nelson Cruz. The Rangers brought in hard-throwing right-hander and Seattle native Keone Kela to face Cruz. The nine-pitch at-bat ended with Cruz swinging and missing at a curveball after fouling off four consecutive pitches.