Beltre finished with three hits and two RBIs, helping the Rangers avoid a three-game series sweep. Mitch Moreland and Elvis Andrus each drove in a run.
With Texas trailing 3-1, Beltre led off the seventh with a drive to center against Hisashi Iwakuma (7-4). A.J. Pierzynski then singled and Lance Berkman walked before Moreland bounced a tying single up the middle against Charlie Furbush.
Andrus came up with a go-ahead sacrifice fly and Ian Kinsler capped the big inning with an RBI single.
Josh Lindblom (1-2) recorded the final two outs of the seventh to pick up his first win since Aug. 31, 2012.
Raul Ibanez homered for the Mariners, belting a tiebreaking two-run shot in the seventh. It was his 12th homer in his last 28 games, lifting the total for the 41-year-old slugger to 21 for the year.
Iwakuma, who came in leading the AL in ERA, allowed four runs and five hits in six innings. The Japanese right-hander is 0-3 with a 5.54 ERA in his last four starts.
Ibanez went 4 for 5 with three RBIs and Kyle Seager added three hits for the Mariners, who were trying for their first series sweep at Texas since 2002.
Ibanez hit an RBI single off Tanner Scheppers in the eighth to get Seattle within one, but Joe Nathan pitched a scoreless ninth for his 28th save in 29 chances.
Beltre picked the perfect time for his 24th multihomer game of his career. The Rangers had scored four or fewer runs in their last six games.
The All-Star third baseman led off the second with his first home run since June 9.
The Mariners tied it with an unearned run in the sixth. Seager and Justin Smoak singled leading off the inning, and Seager scored on a throwing error by second baseman Kinsler, snapping Martin Perez's scoreless stretch at 16 2/3 innings.
Perez allowed an unearned run in 5 1/3 innings. The 22-year-old rookie gave up eight hits, struck out four and walked two in his fourth start of the season.
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