The only hit Kazmir (6-4) gave up was a clean leadoff single to center by Justin Smoak in the fifth. Kazmir struck out seven, walked two and allowed an unearned run. He threw 103 pitches and was relieved by Vinnie Pestano in the ninth. Pestano allowed a hit.
Bourn blew the game open in the fifth with his slam on a full-count pitch from reliever Hector Noesi.
Asdrubal Cabrera had two hits, including his eighth home run. Carlos Santana had three hits, including a pair of RBI doubles. It was the ninth time the Indians have scored at least 10 runs this season and the 14th time Seattle has allowed 10 or more.
Joe Saunders (9-9) took the loss. He lasted just 4 2-3 innings, allowing five earned runs on nine hits, walking three and striking out five. He entered the game with a 4-0 record and 1.73 ERA in his previous four starts and is now 11-4 with a 2.90 ERA in 19 career starts at Safeco Field.
The Indians had lost four of their first five games out of the break and had fallen 3 games behind Detroit in the AL Central.
The loss ended the Mariners' eight-game win streak, their longest since Aug. 14-22, 2012. They were going for their first nine-game streak since May 27-June 5, 2003.
From the first pitch, the Indians -- and Bourn -- had Saunders off-balance. Bourn opened with a drag bunt, easily beating the throw. Nick Swisher walked and Jason Kipnis advanced the runners with a sac-bunt.
Cabrera followed with a two-run double into the left-center gap. Cabrera came home on Santana's ground-rule double to left for a 3-0 score.
The Mariners got a gift run in the second. With two outs and Jason Bay on first, Michael Saunders bounced to shortstop Cabrera. He threw wide of second for an error and Bay raced home.
The Mariners returned the favor in the third when center-fielder Michael Saunders miss-read a Cabrera flyball for a two-base error. Santana drove him home with his second straight double into the left-field corner.
The Tribe rallied in the fifth after two outs. Mark Reynolds singled and Yan Homes walked, ended Saunders' outing. Noesi walked Drew Stubbs and Bourn cranked a fastball over the right-center wall, his third home run.
NOTES: Kazmir has thrown just one complete game in his 198 career starts. That was a two-hit 3-0 shutout on July 3, 2006 with Tampa Bay against Boston. ... Manager Eric Wedge, taken to the hospital before Monday's game because of light-headedness, remains hospitalized while undergoing more tests. "Under the circumstances and all the testing he's going through, it's taking a little longer," said acting manager Robby Thompson. "They're leaning on the cautious side of things." Thompson said he talks to Wedge every day about the team. . Bourn's run in the first inning was the 500th over his career. . Of the 12 games these two teams have played against each other this season, this was the first visitor victory.