Johjima's fourth-inning drive gave the Mariners some breathing room after the A's had pulled within a run. Seattle provided Snell (4-1) with plenty of offense as the right-hander again showed why the Mariners dealt for him just before the trading deadline.
Ken Griffey Jr. returned to the Seattle lineup after missing six games with inflammation in his left knee. He went hitless in four at-bats with a strikeout and said before the game he is considering playing another season if it's the right move for both sides.
The Mariners (71-64) matched a season high by moving seven games over .500, just the second time they've been there all year. Gutierrez also drove in a run in the ninth on a suicide squeeze as Seattle beat the A's for the 13th time in the last 16 meetings in the AL West rivalry dating to Sept. 26, 2008.
David Aardsma pitched the ninth for his 34th save in 38 chances. Seattle wasted no time jumping on Oakland starter Brett Tomko (3-3), who quickly fell behind against his former club.
Gutierrez homered after Ichiro Suzuki's leadoff single in the first, then Hall connected four batters later following a two-out double by Adrian Beltre.
Kurt Suzuki had a two-run single in the bottom of the first for the A's, who scored an unearned run in the second but little else until Daric Barton's solo home run in the eighth. Oakland is coming off consecutive winning series at home for just the third time this season.
The Mariners won their third straight and are approaching the end of a grueling stretch -- this was game No. 30 in a stretch with 33 in 34 days. Seattle, which brought some momentum into the season's final month, started a 10-game road trip on the heels of a 7-3 homestand that began with a three-game sweep of the A's at Safeco Field from Aug. 24-26.
Tomko lost for the first time since being called up from Triple-A Sacramento on Aug. 17, allowing six runs on eight hits in 5 2-3 innings.
Seattle is 10-3 against the A's and has won the season series for the second time in three years. The Mariners improved to 13-6 in California in 2009.
NOTES: Suzuki, who was intentionally walked in the ninth, is 11 hits short of 200 for the year and six shy of 2,000 for his career. The star leadoff hitter returned to the lineup Tuesday after missing eight games with tightness in his left calf. "Ichiro says he feels fine, I'm not sure about 100 percent," manager Don Wakamatsu said. "I talked to him. We'll keep a dialogue going if he needs a day." ... The A's won last year's series with the Mariners 10-9, going 6-3 at home. ... Oakland is 13-24 against the division. ... A's backup C Landon Powell, who hit a grand slam Wednesday, is expected to get another start Sunday.