Iwakuma (10-4), who won his third straight decision, struck out nine and walked one. Since moving into the starting rotation on July 2, 2012, Iwakuma has gone 18-8 with a 2.78 ERA in 38 starts.
Against the Twins, Iwakuma is 4-0 and hasn't allowed an earned run in 26 2-3 consecutive innings over his four starts -- Minnesota's third longest streak. He has held the Twins to a .168 batting average with eight walks and 24 strikeouts.
Felix Hernandez, who starts Friday, has the fourth longest streak at 24 straight scoreless innings.
Nick Franklin hit a three-run home run in the Mariners' big second inning. Dustin Ackley had three hits, including two doubles, and two RBIs.
The Mariners matched a season high with six doubles.
Seattle, which has won nine of 10, has beaten the Twins six straight times at Safeco Field, dating back to May 5 of last season.
Kevin Correia (7-7), chased after just 1 2-3 innings, allowed six runs and seven hits. It was his shortest outing since June 6, 2010, when he also went 1 2-3 with San Diego against Philadelphia.
Six of the first seven Mariners reached with a hit to start the second, and all six scored.
Kyle Seager opened with a double off the right-center wall. Justin Smoak then singled to right.
With one out,
Mike Zunino singled to left to score Seager, Dustin Ackley sent Smoak home with a single to right, Brad Miller's double drove in Zunino, and Franklin hit his eighth homer of the season on 0-2 pitch.
The six runs were the most the Twins have allowed in one inning this season. The Mariners' seven hits were their season high in a frame.
The Twins loaded the bases with one out on two singles and an error in the third but
Trevor Plouffe struck out, and Clete Thomas bounced out to second.
Henry Blanco and Ackley had back-to-back two-out RBI doubles in the fifth for Seattle.
The Twins scored their runs with two outs in the ninth on back-to-back doubles by Chris Herrmann and
NOTES: Robby Thompson, who has managed the past four games in place of Eric Wedge (mild stroke), will fill in for at least nine more games before Wedge is expected to return. ... DH/OF Mike Morse (quad), on rehab at Triple-A Tacoma, could return to the Mariners this weekend. . Twins C
Joe Mauer remained in Minneapolis after his wife gave birth to twin girls on Wednesday. He was placed on the paternity list and C Dan Butera was recalled from Triple-A Rochester. ... Zunino, the Mariners catcher, took a foul tip off his left hand and was removed in the fifth inning for precautionary reasons.