SEATTLE -- Guillermo Heredia isn't known as a good baserunner. He is 1-for-5 on stolen-base attempts this season.

However, the Seattle outfielder raced from first to third on a wild pitch in the bottom of the 13th inning Tuesday, then scored the winning run on Jean Segura's infield single as the Mariners improbably defeated the Boston Red Sox 6-5 at Safeco Field.

Heredia also hit a three-run homer as the Mariners (51-51) returned to the .500 mark and sent the Red Sox (55-47) to their season-high fourth consecutive defeat.

"There were a lot of crazy plays," Mariners manager Scott Servais said.

With Seattle trailing 5-4 one out into the bottom of the 13th, Mitch Haniger walked and Ben Gamel hit into a fielder's choice.

Heredia fouled off a couple of two-strike pitches against Boston's Doug Fister (0-5) before lining a single to right field, with Gamel taking third. Gamel then scored the tying run on the wild pitch, with Heredia advancing from first to third as Red Sox catcher Sandy Leon retrieved the ball near the backstop.

"(Heredia) kept his head up and took the extra base," Servais said.

Red Sox manager John Farrell was asked if Leon lost track of Heredia, the trailing runner.

"I don't know that," Farrell said. "Heredia can fly, so when the ball didn't carom and kick back, when it stayed close to the back wall, he had a chance to take two bases."

Segura then hit a chopper up the middle that Red Sox shortstop Xander Bogaerts raced to his left to field behind second base. Bogaerts tried to make an off-balance throw to first, but even a perfect toss wouldn't have been in time to get the speedy Segura.

"A groundball to the middle of the infield is the difference," Farrell said. "We had opportunities throughout, we fight back from a three-run deficit, but it is what it is. It's a tough loss, but our guys kept grinding."

Tony Zych (5-2), the eighth Seattle pitcher, went two innings to earn the victory.

"You literally go to everybody but one (reliever), you're stretched that thin," said Mariners catcher Mike Zunino, who hit a home run leading off the seventh inning to tie it at 4-4, the last run that scored until the 13th. "To come back and win that way after being down is big."

The Red Sox took a 5-4 lead as Leon singled home the tiebreaking run with two outs in the top of the 13th.

Hanley Ramirez led off with a single that fell just in front of right fielder Haniger. After Zych struck out the next two batters, Ramirez advanced to second on a wild pitch.

After a walk to Chris Young, Leon hit a soft liner to left. Gamel charged the ball and made a strong throw in an attempt to get Ramirez at the plate, but the runner slid home safely as Zunino bobbled the throw.

Staked a 3-0 lead, Seattle right-hander Felix Hernandez cruised through the first five innings, allowing just one run on two hits and throwing just 64 pitches.

However, King Felix never made it out of the sixth, losing his command.

Red Sox rookie third baseman Rafael Devers, making his major league debut and batting ninth, led off with a walk. After Hernandez struck out Mookie Betts on a pitch in the dirt, Andrew Benintendi also walked. Dustin Pedroia followed with a two-run double down the left field line to tie the score at 3-3.

After Ramirez grounded out, Jackie Bradley Jr. lined a run-scoring single into right-center, giving the Red Sox a 4-3 lead.

That was it for Hernandez, who needed 31 pitches to record his only two outs in the sixth.

"Felix was really cruising for five innings, and it got away from him in the sixth," Servais said, citing the bases on balls.

The Red Sox had only one hit until the fourth, when Ramirez hammered a 1-1 pitch from Hernandez off the out-of-town scoreboard in left field. The homer, Ramirez's 17th of the season, was measured at 414 feet.

After a 1-2-3 first inning, Red Sox starter Drew Pomeranz ran into trouble in the second.

With one out, Kyle Seager got an infield single, hitting the ball between first baseman Mitch Moreland and second baseman Pedroia. An out later, Gamel walked before Heredia hit a three-run homer, his sixth of the season. Heredia turned on an 0-1 pitch from Pomeranz and hit it just over the fence down the left-field line for a 3-0 advantage.

Hernandez allowed four runs in 5 2/3 innings, while Pomeranz gave up three runs in five innings.

NOTES: During the game, the Red Sox acquired INF Eduardo Nunez from the San Francisco Giants in exchange for minor league RHPs Shaun Anderson and Gregory Santos. ... Boston 3B Rafael Devers went 0-for-4 with two walks in his major league debut. Seattle DH Nelson Cruz struck out five times in six at-bats. ... Mariners RHP Nick Vincent pitched a scoreless inning of relief to equal a franchise record. Vincent hasn't allowed a run at home this season in 24 appearances, matching the mark set by George Sherrill in 2007. ... Red Sox SS Xander Bogaerts was back in the lineup after missing Monday's series opener with what manager John Farrell called "flu-like stuff." ... LHP Chris Sale (12-4, 2.58 ERA) is scheduled to start for the Red Sox in the series finale Wednesday afternoon against Mariners rookie RHP Andrew Moore (1-2, 5.70).