NBA star Blake Griffin is calling it a career after 14 seasons ... announcing his retirement in a heartfelt post on Tuesday.

The 35-year-old forward was the first overall pick in the 2009 NBA Draft ... spending 7 1/2 seasons with the LA Clippers, where he made the All-Star team 6 times.

Griffin was a high-flying athlete throughout his time on the hardwood ... winning the league's dunk contest in 2011.

"I'm thankful for every single moment," the former Rookie of the Year said on Instagram. "Not just the good ones; the wins, the awards, the dunks, and the memorable times spend with my family, friends, fans, teammates, and coaches."

"I could continue on about the people in my life who have contributed immensely to my career, but in this short non-letter, I have to acknowledge my parents, Tommy and Gail, and my brother, Taylor, for their unconditional support and guidance."

Griffin also shouted out his agent, Sam Goldfeder, for giving him priceless advice throughout his time in the NBA.

"I am equally thankful for the not-so-good moments," Griffin added. "The losses, the injuries, the wayyyy too many surgeries, the lessons, the heartbreaks, and it wouldn't be a sports retirement letter without acknowledging the 'haters.'"

"All of these experiences made my 14 years in the league truly unforgettable, and I can't help but to just feel thankful."

Griffin also played for the Detroit Pistons, Brooklyn Nets and Boston Celtics during his career ... averaging 19 points, 8 rebounds and 4 assists a game.

The hooper is also known for his sense of humor ... so who knows -- maybe he'll take his talents to the mic with all his free time now!!