The 27-year-old Red Sox player let the f-word fly when he stepped into the batter's box during the sixth inning of Boston's blowout loss to Houston.

You can hear in audio from the game's broadcast ... as a man in the Fenway Park stands chirped him about needing "a tennis racket" while at the dish -- he fired back by calling the guy a "f***ing f****t."

Social media users were quick to pick up the clip from the contest and lay into him for the offensive comment -- and after it went viral, Duran said he was sorry.

"During tonight's game," he wrote in a statement, "I used a truly horrific word when responding to a fan. I feel awful knowing how many people I offended and disappointed."

"I apologize to the entire Red Sox organization, but more importantly to the entire LGBTQ community. Our young fans are supposed to be able to look up to me as a role model, but tonight I fell far short of that responsibility. I will use this opportunity to educate myself and my teammates and to grow as a person."

Duran -- who was named All-Star Game MVP in July -- had actually received the Heart and Hustle Award from Boston earlier in the day to recognize him for embodying the "values, spirit and traditions" of baseball.

For their part, the Red Sox said in a statement of their own that they did address the matter with Duran following the game.

"We echo Jarren's apology to our fans, especially to the LGBTQ community," they added. "We strive to be an organization that welcomes all fans to Fenway Park, and we will continue to educate our employees, players, coaches and staff on the importance of inclusivity."